Circular No. 34/2024/TT-BTNMT stipulates technical procedures for building a national geographic base database at a scale of 1:50,000 using echo sounding methods and creating seabed topographic maps from the corresponding national geographic base database.

3. Echo sounding is a method using sound waves to measure water depth.

4. GNSS (Global Navigation Satellite System) is a global satellite navigation system.

5. DGNSS (Differential Global Navigation Satellite System) is a global satellite differential navigation system.

6. RTK (Real Time Kinematic) is real-time dynamic measurement technology.

7. SVS (Sound Velocity Sensor) is a device that measures the speed of sound in water at a specific location, usually installed next to the transducer head of a multi-beam echo sounder to determine the instantaneous speed of sound at the transducer head's position.

8. SVP (Sound Velocity Profiler) is a device that measures the speed of sound in water and records the values of sound speed at different depths, forming a detailed profile of sound speed according to the water depth.

9. Raster is a grid data structure arranged in rows and columns to store digital images. The Raster structure is one of the formats of a digital elevation model, where each cell is referenced by X, Y coordinates and stores a numeric value representing a geographic attribute (elevation value).

10. GDB (Geodatabase) is a format for storing the national geographic base database.

11. GeoTIFF is a digital image file with the extension *.tif attached to the geographic object coordinates in a defined coordinate system.

12. GeoPDF is a data file with the extension *.pdf attached to the geographic object coordinates in a defined coordinate system. The GeoPDF file contains spatial and attribute data of geographic objects.

PART II

RECEIVING NATIONAL GEOGRAPHIC BASE DATABASE AT A SCALE OF 1:50,000

BY ECHO SOUNDER METHOD

Article 4. Mathematical Basis

1. National base geographic data at a scale of 1:50,000 shall be collected uniformly on the National Reference System and National Coordinate System VN-2000, projection zone, central meridian according to the provisions set forth in Circular No. 973/2001/TT-TCĐC dated June 20, 2001 of the Land Administration General Department guiding the application of the National Reference System and National Coordinate System VN-2000.

2. The height system used is the national height system.

Article 6. Preparation Work

1. Prepare necessary surveying equipment including basic surveying equipment such as echo sounder, GNSS receiver, DGPS receiver, electronic compass, acoustic speed meter, wave correction device, and other surveying equipment such as total station, leveling staff, steel tape, automatic tide gauge, time synchronization device. These surveying devices must be checked for stable operation before being put into use. Basic surveying equipment must have technical specifications meeting the following requirements:

a) Single-beam or multi-beam echo sounder with depth measurement accuracy ≤ ± (18 cm + 0.1% h). Where h is the depth measured in meters;

b) GNSS receiver must have the following accuracy:

When measuring statically, planimetric measurement accuracy ≤ ± 5 mm + 0.5 ppm RMS, height measurement accuracy ≤ ± 5 mm + 1 ppm RMS;

When using DGPS, planimetric measurement accuracy ≤ ± 0.25 m + 1 ppm RMS, height measurement accuracy ≤ ± 0.5 m + 1 ppm RMS;

When using RTK, planimetric measurement accuracy ≤ ± 10 mm + 1 ppm RMS, height measurement accuracy ≤ ± 20 mm + 1 ppm RMS;

c) Electronic compass with direction measurement accuracy ≤ ± 0.5°;

d) Acoustic speed meter with acoustic speed measurement accuracy ≤ ± 0.25 m/s;

đ) Wave correction device with wave measurement accuracy ≤ ± 5 cm or 5% of wave height.

2. Prepare computers and software for data acquisition and processing.

3. Contact local authorities and relevant agencies to inform and coordinate implementation. Ensure occupational safety, prepare anchorage sites for vessels, supply plans for food, fuel, and fresh water.

4. Prepare and collect other related documents for the construction area including national base geographic database, national topographic maps, seabed topographic maps, nautical charts at various scales within the measurement area, and other specialized data.

Article 7. Design of Echo Sound Line

1. In case single-beam echo sounder is used

a) Based on seabed topographic map or nautical chart within the measurement area, design echo sound lines. Echo sound lines should be designed prioritizing parallel to the slope direction of the measurement area;

b) The distance between echo sound lines is 500 m on-site. In cases where the seabed terrain in the measurement area has special features such as submarine canyons, underwater volcanoes, steep underwater slopes, or submerged banks, the echo sound lines may be designed with a smaller distance to accurately describe the seabed terrain;

c) If the construction range borders areas that already have national base geographic databases or seabed topographic maps at the same scale or larger scale, the echo sound lines must be designed to ensure a minimum overlap of 500 m with adjacent areas;

d) The direction of the echo sound check lines should prioritize perpendicular to the direction of the echo sound lines. Check lines must be evenly distributed across the measurement area, with the total length of the check lines not less than 10% of the total length of the echo sound lines.

2. In case multi-beam echo sounder is used

Article 8. Construction of Marine Measurement Equipment Inspection Points

1. The marine measurement equipment inspection points must be constructed near the construction area, ensuring convenient connection for measuring height to the "0" point of the water level monitoring station and installation, checking the ship's depth measurement system, or using it as a fixed station in RTK measurement cases.

2. The marine measurement equipment inspection points must be measured and connected to national coordinate and elevation points. The accuracy of coordinates and elevations at the marine measurement equipment inspection points shall be equivalent to those of the first-level control network coordinate and elevation points.

3. The specifications and dimensions of markers, enclosures of marine measurement equipment inspection points shall be implemented according to the provisions of Point 1 of Appendix 1 of Circular No. 68/2015/TT-BTNMT dated December 22, 2015, issued by the Minister of Natural Resources and Environment on direct terrain surveying techniques for the establishment of topographic maps and geographic base data at scales of 1:500, 1:1000, 1:2000, and 1:5000.

4. In cases where there are already national coordinate and elevation points near the construction area, these points may be used as marine measurement equipment inspection points.

Article 9. Installation, Inspection, and Calibration of Marine Measurement Equipment

1. Marine measurement equipment must be inspected and calibrated according to the provisions of Chapter II of Circular No. 27/2011/TT-BTNMT dated July 20, 2011, issued by the Minister of Natural Resources and Environment on the testing and calibration of certain surveying and mapping equipment for marine purposes before being put into use.

2. Installation of Marine Measurement Equipment and Other Devices on Ships

Marine echo sounders and other devices for marine measurements must be installed firmly on ships according to the following technical requirements:

a) The receiving antenna of the DGPS measurement device, digital compass, and wave correction machine must be installed in positions that are advantageous and avoid interference from electromagnetic waves.

b) The transducer head of the echo sounder must be installed submerged at least 0.50 meters below the water surface; the submersion depth of the transducer head must be accurately measured to the centimeter.

c) The wave correction machine must be installed near the ship's center of gravity; the angle deviation between the axis of the machine and the ship's axis must not exceed ± 5 degrees.

d) The digital compass must be installed firmly on a flat surface; the angle deviation between the compass axis and the ship's axis must not exceed ± 5 degrees.

đ) In cases where multi-beam echo sounders are used, an SVS speed measurement device must be installed next to the transducer head to determine the instantaneous sound velocity at the position of the transducer head.

3. Surveying and Accurately Determining the Positions of Installed Marine Depth Measuring Equipment and Other Devices within a Conventional Coordinate System with the Origin at the Ship's Center of Gravity, the Y-axis aligned with the bow direction of the ship, and the X-axis perpendicular to the Y-axis pointing to the right.

4. The positions of the points where the measurement equipment and other devices are placed must be determined at least three times using steel tapes or electronic total stations. Position errors of these points relative to the conventional coordinate origin must not exceed ± 2 cm.

5. Inspect the entire marine depth measurement equipment system: After connecting all equipment and devices to the depth measurement software, the single-beam and multi-beam echo sounder systems must also be inspected and calibrated according to the provisions of Chapter III of Circular No. 27/2011/TT-BTNMT.

Article 10. Water Level Monitoring

1. Water level monitoring stations shall be constructed at locations with free circulation to the sea, minimizing the maximum impact of waves; having stable geological structures that do not cause subsidence or settlement; ensuring safety and convenience for monitoring; guaranteeing operation, stability, and measurement of the lowest and highest water levels throughout the monitoring period. The distance between two adjacent water level monitoring stations shall not exceed 50 km.

2. Point "0" of the water level monitoring station shall be measured and connected to coordinates and heights with marine measuring equipment check points or national coordinate and height points within the construction area. The mean error in determining the coordinates of point "0" of the water level monitoring station shall be ≤ 25 m. The accuracy in determining the height of point "0" of the water level monitoring station shall be equivalent to technical height accuracy.

3. In cases where a water level monitoring station cannot ensure full monitoring of water level changes, additional water level monitoring stations may be built in that area to ensure comprehensive water level monitoring at all times during the measurement process.

4. Use water level monitoring methods with graduated rulers up to cm or automatic tide gauges.

5. Provisions for reading water levels on measuring rulers

a) Water levels shall be read to the cm, fully recorded in the Water Level Monitoring Logbook and used to construct daily water level change graphs;

b) The time interval between two readings of water levels on the ruler is 30 minutes and must be taken at whole hours or half-hour marks. During the 30-minute periods before and after high or low tides, water levels must be read every 10 minutes at 10-minute intervals;

c) At each water level reading time, two readings must be taken, the first reading the water level at the wave base, the second reading the water level at the wave crest; the measured water level value is the average of the two readings;

d) At water level monitoring stations with more than one ruler, when switching from one ruler to another for water level readings, simultaneous readings must be taken on both rulers; the difference in water level reading values on the two rulers shall not exceed 1 cm;

đ) Water level readings must be fully recorded in the Water Level Monitoring Logbook according to Model No. 1 of Appendix II of this Circular.

6. When using automatic tide gauges, the water level data shall be recorded directly on the device with intervals between two recordings not exceeding 10 minutes.

7. In areas without sufficient conditions for direct water level monitoring, numerical tidal models may be used to calculate water level data. The positions of points requiring water level data determination must fall within the construction area and be evenly distributed with a minimum density of 2 points/750 km². Tidal corrections for deep measurement points must use data from at least 2 nearest or most suitable water level data points within the correction range.

Article 11. Seabed Depth Measurement

1. Based on the seabed depth measurement and verification lines designed in accordance with Article 7 of this Circular, seabed topography depth measurements and data collection shall be carried out.

2. Before conducting depth measurements, the submerged head transducer depth must be determined and entered into the depth measurement software. The submerged head transducer depth is the distance from the water surface to the bottom surface of the transducer head, measured to the cm using a steel tape measure. During construction, this value must be regularly checked, especially when there are changes in ship load.

3. Determine the speed of sound in the construction area

a) Within each 1:50,000 scale seabed topography map area, use existing seabed topography maps or charts in the measurement area to determine the deepest location. At each determined position, lower the acoustic speed profiler (SVP) vertically to measure sound speed at different depths. The depth interval between consecutive sound speed data acquisitions is 0.5 m;

b) Sound speed measurement results shall be compiled into a set of sound speed determination results according to Model No. 6 of Appendix II of this Circular;

c) Use the acquired sound speed data by depth to process and calculate depth measurement data within that seabed topography map area.

4. Collecting depth measurement data

a) For single or multi-beam echo sounding along lines, depth measurement data is collected along each measurement line. The allowable deviation between the actual depth measurement line and the design depth measurement line shall not exceed 50 m on-site;

b) For multi-beam swath echo sounding covering the entire seabed, depth measurement data is collected along each swath. During measurement, the design measurement line direction can be changed but must ensure complete coverage of the seabed;

c) Measurement shall only be conducted when the average wave height is ≤ 2 m. If missing or inaccurate depth measurement data is detected, immediate supplementary measurement must be conducted on-site;

d) Throughout the depth measurement process, information about the depth measurement lines and verification measurements must be fully recorded in the Depth Measurement Logbook according to Models No. 3 and No. 4 of Appendix II of this Circular.

5. The positions of depth measurement points shall be determined using DGPS or RTK technology. In areas where depth measurement does not receive DGPS correction signal or cannot apply RTK technology, leased correction signals from service providers may be used, but must ensure the positioning accuracy specified in Clause 6 of this Article.

6. The mean error in determining the planar position of depth measurement points shall not exceed 15 m.

a) ± 0.3 m when the depth is up to 30 m;

b) 1.5% of the depth when the depth is from over 30 m to 100 m;

c) 2.5% of the depth when the depth exceeds 100 m.

Where:

m: mean error of the depth of the depth measurement point

n: number of check points

Δ: depth difference determined as follows:

- When using single-beam or multi-beam echo sounders along lines, Δ is the difference between the depth measurement line and the verification line at their intersection; the depth at this intersection is interpolated from the two nearest depth measurement points before and after the intersection on each line.

- When using multi-beam echo sounder equipment to measure seabed depth and cover the entire seabed terrain, Δ is the difference in depth of overlapping points in the data between two adjacent scan strips; the depth at these points is derived from the data of each scan strip on a grid with a size of 25 m x 25 m.

8. The depth measurement error must not exceed 2.5 times the root mean square error. The number of check points with errors greater than 2.0 times the root mean square error must not exceed 5% of the total number of check points. In all cases, errors must not be systematic.

9. For coastal areas where it is impossible to measure depth using echo sounders, depth measurement can be carried out using one of the following methods:

a) Using a depth pole marked in centimeters to measure depth. Depth readings are taken from the pole to the nearest centimeter and tidal corrections must be applied to the depth data. The coordinates of the depth measurement point are determined using DGNSS technology. The depth and coordinates of the depth measurement points using the pole must be fully recorded in the Pole Measurement Logbook according to Model No. 2 in Appendix II of this Circular;

b) When using RTK technology to determine the coordinates and heights of detailed seabed topography points, it shall be implemented in accordance with Article 28 of Circular No. 68/2015/TT-BTNMT dated December 22, 2015 issued by the Minister of Natural Resources and Environment regarding technical procedures for direct surveying of seabed topography for the purpose of creating topographic maps and geographic base databases at scales of 1:500, 1:1000, 1:2000, and 1:5000; in cases where national satellite positioning network data services are used, implementation shall follow the provisions of Article 21 of Appendix 09 and Appendix 10 of Circular No. 03/2020/TT-BTNMT dated May 29, 2020 issued by the Minister of Natural Resources and Environment regarding technical regulations for the national satellite positioning network and Article 29 of Circular No. 68/2015/TT-BTNMT.

10. When conducting seabed topography depth measurements as stipulated in Clause 9 of this Article, priority should be given to collecting depth measurement points at locations where there are changes in topography to accurately and comprehensively represent the surface of the seabed. In all cases, the density of depth measurement points must reach from 25 to 30 points per 1 km².

Article 12. Sampling Seabed Material

1. Sampling of seabed material may only be conducted upon specific project requirements. Seabed material samples are collected using a scoop, tube, or combined with sonar image interpretation methods.

2. The sampling density must ensure that at least one sample is taken per 25 km² and evenly distributed over the construction area.

3. The determination of the sampling location for seabed material is regulated similarly to the determination of the measurement location for depth points as specified in Clause 5 of Article 11 of this Circular. The root mean square error in determining the planimetric position of the sampling points must not exceed 15 meters. The actual location of the sampling point compared to the design must not exceed 20 meters.

4. Seabed material samples are analyzed on-site and images of the samples are retained. If necessary, samples must be stored for laboratory analysis. Information about the seabed material samples must be fully recorded in the Seabed Material Sampling Logbook according to Model No. 5 in Appendix II of this Circular.

Article 13. Collection of Attribute Data of Geographic Objects and Depth Compensation

1. In addition to the geographic objects whose spatial and attribute information is fully collected through echo sounding and sampling methods, other geographic objects specified in Appendix I of this Circular must be fully collected for their positions and accompanying attribute information from the documents prepared as stipulated in Clause 4 of Article 6 of this Circular or collected simultaneously during depth measurement or by the surveying methods specified in Clause 9 of Article 11 of this Circular, according to the following principles:

a) For geographic objects floating on the water surface or partially submerged, their positions are determined using GNSS, and their heights can be determined using GNSS, steel tape, or trigonometric leveling. Partially submerged geographic objects are measured and positioned when they are most visible on the water surface;

b) For geographic objects that can be drawn to scale, the positions of their outlines and centers must be determined; in cases where the geographic object has a small area and cannot be drawn to scale, its center must be determined directly through measurement or indirectly through calculation;

c) For completely submerged geographic objects, their shape and position are measured and determined as specified in Clause 2 of this Article.

2. In cases where single-beam echo sounders are used, if special seabed terrain or objects are discovered during measurement and require increased density of depth measurement points to detail the seabed terrain surface, depth compensation must be performed. Depth compensation is carried out similarly to seabed topography depth measurement but with distances between adjacent measurement lines ranging from 25 m to 50 m depending on the detected object, and only within the scope of the special seabed terrain or object.

Article 14. Processing of depth measurement data and establishing digital elevation models

1. Depth measurement data after collection must be reviewed and abnormal value points removed before processing and calculation.

2. Processing of depth measurement data

a) Use water level observation data collected according to Article 10 of this Circular to perform tidal correction for depth measurement data and verification depth measurement data;

b) After tidal correction, depth measurement data and verification depth measurement data must be compiled so that at each detailed depth measurement point there are coordinate values and elevations to serve checking and evaluating the accuracy of the depth measurement point according to 4.2.2, 4.2.3, 4.2.4 Part II of QCVN 70:2022/BTNMT National Technical Regulations on national topographic maps at scales of 1:50,000 and 1:100,000 issued together with Circular No. 06/2022/TT-BTNMT dated June 30, 2022 of the Minister of Natural Resources and Environment. For single-beam echo sounder depth measurement data, only areas with a terrain slope of 5 degrees should be checked. The results of checking and evaluating the accuracy of the depth measurement point are compiled into a file of depth measurement data check results according to Model No. 7 Appendix II of this Circular;

c) After the accuracy of the depth measurement data has been evaluated and meets requirements, it is necessary to export the data along each depth measurement line based on the principle that the distance between two consecutive depth measurement points does not exceed 100 meters for single-beam echo sounder data and in a grid format of 25 meters x 25 meters for multi-beam echo sounder data.

3. Establishing a digital elevation model

a) The digital elevation model is established from processed depth measurement data at point c clause 2 of this Article;

b) The accuracy of the digital elevation model to be established shall be implemented according to the provisions in Section B.5 of Appendix B of QCVN 71:2022/BTNMT National Technical Regulations on national geographic base data at scales of 1:50,000 and 1:100,000 issued together with Circular No. 07/2022/TT-BTNMT dated June 30, 2022 of the Minister of Natural Resources and Environment.

4. Depth Measurement Data and Digital Elevation Models

a) Depth measurement data after being exported along each depth measurement line is compiled in a unified format (X, Y, h).

Where:

X, Y: coordinates of the depth measurement point;

h: elevation of the depth measurement point.

b) The product of the digital elevation model has formats Raster (GeoTIFF-32 bit) and ASCII. The digital elevation model product must be checked to meet quality standards as stipulated in Section C.4.4 of Appendix C of QCVN 71:2022/BTNMT.

Chapter III

BUILDING NATIONAL GEOGRAPHIC BASE DATA AT SCALE 1:50,000 FROM ECHO SOUNDER DEPTH MEASUREMENT DATA

Article 15. Procedure for building national geographic base data at scale 1:50,000 from echo sounder depth measurement data

Building national geographic base data at scale 1:50,000 from echo sounder depth measurement data is carried out according to the following procedure:

Figure 2: Flowchart for building national geographic base data at scale 1:50,000 from echo sounder depth measurement data

Article 16. Review, classification, and compilation of data content

1. Use the digital elevation model established in clause 3 of Article 14 to interpolate basic contour lines, half-interval contour lines, and supplementary contour lines according to Section B5 of Appendix B of QCVN 71:2022/BTNMT.

2. Use depth measurement data to filter depth points and annotate depths with a density of approximately 20-25 points per square kilometer. Use the digital elevation model to extract additional characteristic depth points of the terrain.

3. Conduct review, classification of geographic objects collected according to each group of classes, geometric data types, and attributes as stipulated in Article 3 of Part II and Appendix A of QCVN 71:2022/BTNMT.

4. After classification, compile geographic object data. During the compilation process, geographic objects must be accurately positioned and spatial relationships between objects must comply with the provisions of Article 4 of Part II of QCVN 71:2022/BTNMT.

5. The product of this work step is data files that have been reviewed, classified, and content compiled, meeting conditions for entry into the national geographic base database.

Article 17. Establishing the National Geographic Base Database

1. Create the framework of the National Geographic Base Database using specialized software. The newly created framework data file includes empty data packages and layers with a structure model implemented strictly according to the provisions of Article 2 Part II of QCVN 71:2022/BTNMT to serve the entry of national geographic base data content. The product of this work step is the National Geographic Base Database framework file in GDB format.

2. In cases where the geographic object type in the structure model specified in Article 2 Part II of QCVN 71:2022/BTNMT has 01 spatial attribute, name the database layer according to the following principle:

a) The layer name is the geographic object type name specified in Article 2 Part II of QCVN 71:2022/BTNMT.

b) Name the Vietnamese alias (Alias) of the geographic object type specified in Article 2 Part II of QCVN 71:2022/BTNMT corresponding to the geographic object type name specified in Appendix B of QCVN 71:2022/BTNMT.

3. In cases where the geographic object type in the structure model specified in Article 2 Part II of QCVN 71:2022/BTNMT has 02 or more spatial attributes, name the database layer according to the following principle:

a) The layer name is the geographic object type name specified in Article 2 Part II of QCVN 71:2022/BTNMT, simultaneously adding the corresponding data type abbreviation specified in Article 5 Part I of QCVN 71:2022/BTNMT.

b) Name the Vietnamese alias (Alias) of the geographic object type specified in Article 2 Part II of QCVN 71:2022/BTNMT corresponding to the geographic object type name specified in Appendix B of QCVN 71:2022/BTNMT, simultaneously adding the Vietnamese equivalent of the data type specified in Article 5 Part I of QCVN 71:2022/BTNMT.

4. Enter reviewed, classified, and content-edited data according to the provisions of Article 16 into the National Geographic Base Database framework file using specialized software to establish the National Geographic Base Database. During implementation, monitor to ensure that all data is fully entered into the National Geographic Base Database.

5. For areas building the National Geographic Base Database adjacent to land, islands, or island groups already having a National Geographic Base Database at the same scale, collect and enter into the National Geographic Base Database framework to ensure seamless integration and ensure complete coverage when creating maps. If these areas only have databases at scales larger than 1:50,000, it is necessary to generalize them to the 1:50,000 National Geographic Base Database scale.

Article 18. Standardizing the National Geographic Base Database

1. Data entered into the National Geographic Base Database framework is standardized according to the structure model specified in Article 2 Part II of QCVN 71:2022/BTNMT.

2. The standardization content includes: completeness of data; suitability of data with the data structure model; accuracy of geographic object location; accuracy of geographic object time; accuracy of thematic attributes. The standardization results must meet all component criteria specified in Section C.1 of Appendix C of QCVN 71:2022/BTNMT.

3. In cases where the scope of establishing the National Geographic Base Database borders with existing National Geographic Base Databases, data integration must be carried out according to the provisions of 4.3 Part II of QCVN 71:2022/BTNMT.

Article 19. Presentation of the National Geographic Base Database

The presentation of the National Geographic Base Database shall be carried out in accordance with the provisions of Article 5, Part II of QCVN 71:2022/BTNMT. The product of this work step is the presentation data file accompanying the standardized National Geographic Base Database as stipulated in Article 18 of this Circular.

Article 20. Construction of Metadata

1. The content of metadata shall be implemented according to the provisions of Appendix I of QCVN 42:2020/BTNMT, the National Technical Regulation on Basic Geographic Information Standards issued together with Circular No. 06/2020/TT-BTNMT dated August 31, 2020 of the Minister of Natural Resources and Environment. The process of constructing metadata must comply with the National Standard TCVN 12687:2019 Geographic Database - Construction of Metadata published pursuant to Decision No. 3281/QĐ-BKHCN dated November 6, 2019 of the Minister of Science and Technology regarding the publication of the National Standard. The product of this work step is the packaged metadata file in the ISO 19139 XML format.

2. Metadata shall be constructed and integrated with the National Geographic Base Database at the levels of database and dataset.

Article 21. Packaging of the Database

1. The National Geographic Base Database at a scale of 1:50,000 shall be packaged within the scope of the boundary of the area for building the National Geographic Base Database. Data formats shall comply with the provisions from 1.3 to 1.6 of Part II of QCVN 71:2022/BTNMT.

2. The products shall be recorded on storage devices, and the labels of these storage devices must include all basic information and be legally confirmed, including: Scope and scale, name of the project sponsor, name of the construction unit, name of the quality inspection unit, time of product submission. In cases where the submitted products are recorded on multiple storage devices, each storage device must clearly indicate its serial number among the total number of submitted storage devices. Packaging of the database shall be conducted in accordance with Appendix VI of this Circular.

Chapter IV

ESTABLISHING THE NATIONAL TOPOGRAPHIC MAP OF THE SEABED AT A SCALE OF 1:50,000 FROM THE CORRESPONDING NATIONAL GEOGRAPHIC BASE DATABASE

Article 22. Procedure for Establishing the National Topographic Map of the Seabed at a Scale of 1:50,000 from the Corresponding National Geographic Base Database

The establishment of the national topographic map of the seabed at a scale of 1:50,000 from the corresponding national geographic base database shall be carried out according to the following procedure:

Diagram 3: Flowchart for Establishing the National Topographic Map of the Seabed at a Scale of 1:50,000 from the Corresponding National Geographic Base Database

Article 23. Preparation Work

1. Prepare computer equipment, software with functions to edit the national topographic map from the national geographic base database, and other related equipment.

2. Prepare the national geographic base database at a scale of 1:50,000 for the area required to establish the national topographic map of the seabed.

3. Prepare the library of numerical symbols for the national topographic map at a scale of 1:50,000.

Article 24. Display Presentation of the National Topographic Map of the Seabed at a Scale of 1:50,000

1. Based on the national geographic base database, assess the characteristic features of the area required to establish the national topographic map of the seabed according to criteria related to terrain and land objects, including: seabed slope, areas with land, islands, or only sea, to develop appropriate technical editing materials.

2. On the basis of the results of the survey and evaluation of the national geographic base database mentioned above, develop technical editing materials to meet the requirements for editing and presenting maps as prescribed. Develop detailed application guidelines for each area.

3. Present the geographic objects in the national geographic base database according to the principle that the geographic object and its attribute information will be linked to the corresponding symbol in the library of numerical symbols for the national topographic map. The principle of presenting geographic objects according to the symbols of the national topographic map at a scale of 1:50,000 is specified in Appendix III of this Circular.

4. The groups of layers of the national topographic map of the seabed are named and arranged in the following display order:

a) Mathematical base layer group;

b) National border and administrative boundary data layer group;

c) Transportation data layer group;

d) Hydrographic data layer group;

đ) Population data layer group;

e) Terrain data layer group;

g) Vegetation cover data layer group.

5. Within each group of layers of the national topographic map of the seabed, the display order of the data layers is as follows:

a) Layer of names and annotations of geographic objects in that data layer group;

b) Layers of geographic objects with point data type;

c) Layers of geographic objects with line data type;

d) Layers of geographic objects with polygon data type;

đ) Each layer is displayed in sequence according to the order specified in Appendix III of this Circular.

6. Rules for presenting names and annotations for geographic objects

a) Names and annotations of geographic objects are presented in a layer and displayed based on the name attribute and attributes containing information to be annotated on the national topographic map of the seabed as stipulated from 2.2 to 2.9 of Part II of QCVN 70:2022/BTNMT;

b) Names and annotations of point-type geographic objects are prioritized to be presented to the right of the symbol, based on the size of the symbol to determine the distance from the center of the symbol to the appropriate placement of the name and annotation, ensuring a distance of 0.5 mm from the outer edge of the symbol to the position of the name or annotation on the map. For point-type objects such as height points or depth points, the distance from the point to the position of the annotation is 0.3 mm;

c) Names and annotations of line-type geographic objects are placed on the geographic object itself and repeated at intervals of 10 cm to 15 cm on the map;

d) Names and annotations for polygon-type geographic objects are placed at the center of the polygon;

đ) Do not display names and annotations for military camps, headquarters, defense works;

e) Do not display names for coordinate points, state heights, and measurement base points.

7. Preliminary Evaluation of the Display Presentation Results of the National Topographic Map of the Seabed

a) After displaying the content elements of the national topographic map of the seabed, it is necessary to evaluate the compliance of each map fragment with the content representation regulations from 2.2 to 2.9 of Part II of QCVN 70:2022/BTNMT;

b) In the case where most of the names and annotations on the map are appropriate, record the results to serve as the basis for preparing technical editing guidance documents.

c) In cases where there are still many names and annotations on the map that do not comply with regulations or overlap each other, it is necessary to re-perform the work step set out in Clause 6 of Article 24 of this Circular based on resetting parameters appropriately.

Article 25. Editing of marine topographic maps at a scale of 1:50,000

1. The editing of marine topographic maps at a scale of 1:50,000 shall be carried out within the scope of individual map sheets and technical editing documents, ensuring compliance with the technical requirements regarding content and symbols of national topographic maps at a scale of 1:50,000 as stipulated in QCVN 70:2022/BTNMT.

2. Editing of map symbols

a) Editing of groups of map symbols shall be performed if the presentation displayed in Article 24 of this Circular does not meet the requirements of national topographic maps at a scale of 1:50,000.

b) When there are multiple overlapping geographic objects or objects that are too close to each other, the editing shall be carried out according to 2.2.8 Part II of QCVN 70:2022/BTNMT.

c) In cases where linear objects use symbols of the same color as letter symbols or independent symbols and cannot be moved, it is permissible to break the linear objects to create a distance of 0.2 mm between symbols on the map to clearly distinguish two symbols of the same color.

d) In cases where small area objects represented by spreading symbols over regions must ensure the display of at least one representative symbol in the center of the region.

đ) For the group of traffic data layers, it is necessary to edit: slope protection symbols placed along the direction of the terrain slope; non-proportional symbols must be placed along the direction of the traffic route; natural conservation area symbols, aquaculture zone symbols, and marine prohibition area symbols must be edited to ensure completeness and clarity of symbols.

e) For the group of hydrographic data layers, additional flow direction symbols and tidal current direction symbols should be created, with flow direction and tidal current direction symbols placed at positions suitable to the terrain slope. Symbols for embankments, shorelines, and slope protection structures should be placed along the direction of the terrain slope; symbols for areas such as riverbank alluvial plains, coastal lakes, swamps, and underwater rocks must follow the directions specified in Appendix B of the Symbols of National Topographic Maps at a Scale of 1:50,000 in QCVN 70:2022/BTNMT; coral reef symbols must be edited to ensure completeness and clarity.

g) For the group of population data layers, attention should be paid to editing beach resorts, tourist areas, oil drilling platforms, oil and gas extraction towers accurately to their positions. Seabed infrastructure technical facilities such as submarine power cables, submarine telecommunications cables, and submarine oil pipelines, if required to be shown, must be edited correctly, completely, and clearly.

h) For the group of topographic data layers, additional contour gradient line symbols for depth level lines should be created, with contour gradient line symbols placed at positions suitable to the terrain slope. Editing must be done correctly according to the direction of symbols for special seabed features represented proportionally or non-proportionally.

i) For the group of vegetation cover data layers, sufficient symbol lines must be edited within the range of vegetation areas after spreading symbols over regions.

3. Editing of names and annotations

a) If the names and annotations of geographic objects presented in Article 24 of this Circular do not comply with the requirements of national topographic maps at a scale of 1:50,000, they must be edited according to the regulations.

b) Check, review, and edit the names and annotations of linear objects throughout the entire area.

c) For linear objects represented by proportional symbols with sufficient width to display names and annotations, they should remain unchanged.

d) For linear objects represented by half-proportional symbols, it is necessary to edit, move the names and annotations of these linear objects up or down the object considering the density of nearby geographic objects to avoid overlapping.

4. The orientation of names and annotations shall be implemented according to the following principles:

a) When the direction of the geographic feature is East-West, the head of the characters faces North.

b) When the direction of the geographic feature is North-South, the head of the characters faces West.

c) When the direction of the geographic feature is Northwest-Southeast, the head of the characters faces Northeast.

d) When the direction of the geographic feature is Northeast-Southwest, the head of the characters faces Northwest.

đ) In cases where linear objects have a long curved shape, the head of the characters faces North.

e) In cases where names and annotations touch, stick together, or overlap, the position of the names and annotations of these geographic objects should be moved according to the priority order specified in Appendix IV of this Circular.

5. In cases where the density of names and annotations is too high, affecting the quality, content, and capacity of the topographic map, the editing should be carried out in the following steps:

a) Review the names of geographic objects occupying large areas on the map and abbreviate common terms according to the provisions in Appendix C of QCVN 70:2022/BTNMT.

b) Select and retain names and annotations for important, famous, or directional geographic objects.

c) After completing the above editing steps, if the density of names and annotations still affects the presentation of the map, it is permissible to reduce the font size to two-thirds of the prescribed size in the symbols.

6. For geographic objects located on two or more map sheets, attention should be paid to editing to fully display the names and annotations of these geographic objects on the respective map sheets in accordance with the regulations.

7. Editing and presenting the map frame shall comply with the provisions in 2.3 Part II and Appendix D of QCVN 70:2022/BTNMT. For map sheets that only contain sea areas, explanations for land and island geographic objects shall not be shown.

Article 26. Publishing maps according to product formats specified

1. Exporting seabed topographic map data files to GeoTiFF - 24 bit format.

2. Exporting seabed topographic map data files to GeoPDF format with 300 dpi resolution. GeoPDF data must be separated into individual layers as prescribed in Part II.2 of Appendix VI of this Circular.

Article 27. Building metadata for maps

1. Building metadata for maps is the final step after completing the editing contents of seabed topographic maps.

2. Metadata content shall comply with the provisions set out in Appendix I of QCVN 42:2020/BTNMT. Implement building metadata according to the model prescribed in Appendix V of this Circular. The product of this step is an XML ISO 19139 formatted metadata file.

3. After completing the metadata construction, quality check of the metadata must be conducted before integrating it into the digital seabed topographic map data file as stipulated in Article 26 of this Circular.

Article 28. Packaging map products

1. Seabed topographic map products at Article 26 of this Circular and intermediate products, which are national geographic base databases used to establish national topographic maps in GDB format, and national topographic map presentation files in MXD format, shall be packaged according to the map sheet version number and accompanied by technical editing documentation.

2. Submitted products shall be recorded on storage devices, with storage device labels containing all basic information and confirmed for legal validity, including: map sheet version number, name of the project investor, name of the implementing unit, name of the quality control unit, submission date of the product. In cases where submitted products are recorded on multiple storage devices, each storage device must clearly indicate its serial number among the total number of submitted storage devices. If the list of map sheet version numbers within the area required for map establishment cannot be fully displayed on the storage device's surface, they shall be recorded on A4 paper and attached to the storage device. Map products shall be packaged according to the provisions set out in Appendix VI of this Circular.

CHAPTER V

IMPLEMENTING PROVISIONS

Article 29. Effective Date

1. This Circular takes effect from January 31, 2025.

2. Decision No. 03/2007/QĐ-BTNMT dated February 12, 2007, issued by the Minister of Natural Resources and Environment, establishing technical regulations for the creation of seabed topographic maps at a scale of 1:50,000, shall cease to be effective from the date this Circular takes effect.

Article 30. Transitional Provisions

1. For work contents related to surveying and creating seabed topographic maps at a scale of 1:50,000 that are being implemented prior to the effective date of this Circular, continue to implement according to Decision No. 03/2007/QĐ-BTNMT dated February 12, 2007, issued by the Minister of Natural Resources and Environment, establishing technical regulations for the creation of seabed topographic maps at a scale of 1:50,000.

2. Work contents initiated from the effective date of this Circular shall be implemented according to the provisions of this Circular.

Article 31. Implementation Organization

1. Ministries, ministerial-level agencies, government agencies, provincial People's Committees under central cities, and relevant organizations and individuals are responsible for enforcing this Circular.

2. The Vietnam National Survey and Mapping Center is responsible for disseminating and supervising the implementation of this Circular.

3. During implementation, if there are any difficulties, agencies, organizations, and individuals are requested to promptly report to the Ministry of Natural Resources and Environment for consideration and decision.