Discussion on updating technology of basic maps and data of land use

Updating basic maps and data of land use is a basic work of land and resources management. At present, some counties in China have carried out the project of updating the basic map data of land use, and Xiyang County, Shanxi Province, as the first batch of pilot counties in China, has carried out this work. During the implementation of the project, under the premise of strictly implementing the technical specifications such as land use survey and daily cadastral management measures (rural areas), the county adopted new technologies and new means to deeply discuss and study the technical route, technical methods and technical measures for updating land basic maps and data.

The technical idea of 1

Xiyang County is located in the east of Shanxi Province, at the west foot of Taihang Mountain. It used to be the location of Dazhai, a model of national agricultural development in the 1960s and 1970s. The territory is a typical rocky mountainous area with undulating mountains, criss-crossing gullies and complex landform types. The total land area of the county is 1952 square kilometers, including 33738+05 hectares of cultivated land; The county has a population of 245,000, with per capita land of 0.8 hectares and per capita cultivated land of 0. 14 hectares. It is a mountainous county with vast land resources and insufficient cultivated land resources. In the face of complex terrain conditions, before the implementation of the project, the technical scheme and route should be formulated first, and the operation process should be stipulated.

1. 1 technical scheme

The guiding ideology of formulating the technical scheme is: make full use of the existing detailed land survey results and land change investigation results, combine the requirements of the "Digital Land" project, adopt the existing high-tech and latest basic geographic information, give consideration to economy and feasibility, explore new technologies and new means, conduct comprehensive field verification, and finally form a set of digital maps and data with consistent maps, numbers and fields.

After full investigation, three sets of technical schemes were determined for selection: ① Using advanced satellite remote sensing technology to complete the project, that is, purchasing high-resolution and panchromatic remote sensing data, using digital photogrammetry system to identify, classify and edit cadastral images (or land-type images) and other image data, establishing a three-dimensional land use status model, compiling a land use status map and establishing a land use database. (2) Purchase orthophoto map, and complete it through field verification in combination with the "Digital Land" project. The aerial photographs of 23 cm×23 cm taken in Shanxi Province in recent years cover nearly 80% of the orthophoto map of Xiyang County. These data can be used to complete the task of updating the basic map and data of land use. (3) Using topographic maps and aerial photographs to complete this project, the original technical route of detailed land investigation is basically adopted.

The above three schemes have high technical content, but the data are expensive and difficult to obtain, which is difficult to realize for Xiyang, an economically underdeveloped mountainous county. ② The scheme has high technical content, strong operability, low system risk and technical and economic feasibility. (3) The scheme still follows the technical route of detailed land investigation, with low technical content, which cannot reflect the principle of innovation. In addition, the topographic map of Xiyang county has not been updated since 1975, and the surveying and mapping accuracy is low, and the topography changes greatly, so it is difficult to correspond to the base map. Updating the basic map and data of land use on this base map is technically infeasible and fails to achieve the expected purpose.

After extensive consultation, the second scheme is adopted, which has high technical content, is innovative in the combination of new technology with existing detailed investigation results and land change investigation results, is economical and feasible, and can provide reference experience and working mode for updating basic maps and data of land use in northern mountainous counties.

1.2 technical route

Under the general control of the technical scheme, a feasible and reliable technical route has been worked out, that is, 1∶ 10000 standard framing orthophoto map, standard kilometer grid map, and 197 film map marked with boundaries, villages, major rivers, roads and other features as the base map of field investigation. According to the specific requirements of Technical Specification for Investigation of Land Use Status in Shanxi Province, Measures for Daily Cadastral Management, and Implementation Plan for Field Investigation, and referring to the results of detailed land investigation, aerial photography was carried out on the fuzzy part of local orthophoto map, and all-field land type mapping and ownership boundary investigation were carried out, and supplementary investigation was carried out on new features. According to the national database construction standard, a set of scientific and complete land use database is established by using MapGis software. The specific steps are as follows:

(1) Purchase1:1000 standard framing orthophoto map and its supporting digital map data, purchase part of the latest aerial photo data, form a digital image map after professional correction, and output a set of1:10000 standard framing orthophoto map.

(2) Classify the original land survey data and land change survey data, analyze their scientificity and present situation, make full use of the original survey results, and carefully design and print the contents of the verification work form. The design of the worksheet not only considers the connection with detailed land survey data and land change survey data, but also considers the design, compilation and establishment of land use database system, and fully considers the use and update of future data.

(3) Select two towns and villages, and the members of the technical guidance group will lead the operators to conduct "actual combat drills" on the spot, hold technical training courses, and train the field survey operators, then make full use of the existing data to conduct on-the-spot verification, fill in the work form, measure the width of the ridge, and at the same time draw a film map of the special elements of land use status on the orthophoto map.

(4) Check and analyze the pictures to see if there are any new features on the pictures, whether the sporadic types are reasonably deducted, and whether the map arrangement meets the requirements.

(5) Digitize the thematic elements of land use and related map elements according to the requirements of database construction. Overlay and edit to form a graphic data file of land use status, and print out1:1000 standard framing land use status map,1:1000 free framing land use status map and1:50000 county-level land use status map.

(6) Input the data in the worksheet into the land use database management system, which is related to the land use graphic database through the geographic information coding system, and a new set of area data is automatically generated by the microcomputer, thus establishing a complete land use database management system.

(7) Write technical and work summary, report the revised and improved results and file them for later use.

2 technical methods

The project adopts the technical method of combining field investigation with indoor database construction.

2. 1 field investigation

First of all, Shanxi Institute of Basic Geographic Information provided1:10000 standard framing orthophoto map and1:10000 km grid map as working maps for field investigation. Land use status1:10,000 standard framing topographic map as a reference for field adjustment.

The field investigation takes the administrative village as the investigation unit, and under the guidance of the soil administrators and village guides in each township, the standard framing image map of 1∶ 1 0,000 is fixed on the drawing board for field investigation, and the investigators draw the thematic elements of land use status quo on the image map with pencils. After a field investigation in an administrative village, external adjustment and painting will be carried out in time. The survey content is colored with drawing ink, and the thematic elements of land use status are drawn on the image map. At the same time, fill in the ownership boundary agreement and field investigation work sheet, including field investigation record sheet, linear feature measurement record sheet, enclave notice, etc. If the ownership boundary is disputed, fill in the land dispute reason book, then cover the corresponding kilometer grid map on the 1: 10000 standard frame image map, and use drawing ink for color separation and clear drawing.

2. 1. 1 boundary and land ownership boundary mapping

Investigators assigned demarcation personnel from two neighboring parties to the site to demarcate and draw at the same time. Both parties call the same border as an uncontroversial border, and fill in the land ownership border agreement. The main contents are as follows: ① Attached drawing. Determine the inflection point of the ownership line; 2 text description. Explain the true position of inflection point and ownership boundary; ③ Signature and seal of all parties. If the boundaries referred to by both parties are different, the land between the two boundaries is disputed land, and the reasons for the land dispute should be filled in, as follows: ① Attached Figure. Clarify the inflection point of the boundary between the two sides; 2 text description. Explain the true location of inflection point and ownership boundary, the reasons for the dispute and the documents provided; ③ Signature and seal of all parties.

When the land ownership boundary coincides with the boundary, the boundary shall be demarcated. When two or more administrative boundaries overlap, only high-level boundaries are drawn. If the linear elements belong to the adjacent cells * * *, the boundaries are drawn alternately at intervals of 0.2 mm on both sides of the linear element symbols. If a linear feature is owned by a company, the boundary is drawn every 0.2 mm along one side.

Punch out the exact position of inflection point of boundary and ownership boundary on the orthographic image (the aperture of inflection point is 0. 1mm), circle the inflection point on the back, describe it in words, and mark the signature of the demander and the date of drawing.

2. 1.2 topographic mapping

The basis of map division: ① land classification is based on the current land use classification and the final classification of the meaning table (from the "Regulations on Land Use Survey"); ② Units with different ownership; (3) Natural cutting of main linear elements.

Category boundaries are indicated by solid lines. When the local boundary coincides with linear features or boundaries and land ownership boundaries, it can be omitted. The number of patches is in the form of numerator and denominator, where numerator is patch number and denominator is land type number, that is, patch number/land type number.

1:110,000 standard frame image map, the minimum upper Tu Tu point area is 4.0mm2 for residential land, 6.0mm2 for cultivated land, gardens and waters, and 15.0mm2 for other land types. The actual area of land types smaller than the minimum sampling point should be recorded as sporadic land types, and the minimum recorded area is 100 square meters, and sporadic land types smaller than 100 square meters are not recorded.

Measure 2. 1.3 ridge

According to the fact that there are many acres of cultivated land in Xiyang County, the measurement of acres is deducted by calculating the coefficient. Measure the actual width and length of the ridges of all the measured sample points on the orthographic image. According to the landform types, each landform type area is divided according to the slope, and the ridge coefficient of each grade is obtained. The county is divided into three landform types: soil mountainous area, rocky mountainous area and hilly mountainous area, and each landform type area is divided into four slope grade areas, so the county is divided into 12 slope grade area. Select 2% ~ 4% representative map spots not less than 15 mu in each slope area, measure the area of each ridge on the spot, fill in the record sheet on the spot, and calculate the ridge coefficient of each slope area. Fill the calculated ridge coefficient into the field record table respectively.

2. 1.4 linear topographic mapping

Linear elements include rivers, highways, railways, forest belts, ditches and canals. When its width is greater than or equal to 2 meters, it should be adjusted and measured on site, and its point should be marked on the schematic diagram, and the measurement should be accurate to 0. 1 meter. Linear elements with large width changes should be measured in sections.

Large rivers with a width of more than 25 meters can be numbered directly without field measurement. If the map width is less than 2.5 mm, it will not be treated as a separate map point, and the linear feature area will be deducted from the corresponding map point.

You can choose rural roads below the level of rural roads for important surveying and mapping, and the rest only record the area (according to sporadic land types), measure the width on the spot, measure the length on the construction drawing, calculate its area, and then fill in the corresponding linear element measurement record form and field investigation record form for registration. Provincial roads, national roads and railways shall be subject to the documents and maps provided by the county.

Ditches are generally surveyed and mapped above main canals and branch canals. For important surveying and mapping, you can choose the following bucket canals, agricultural canals and Mao canals (referring to those with a width of more than 2 meters). The rest are field measurements, only recording the area without drawing.

2. 1.5 supplementary survey features

When the actual features change, make up the survey, focusing on the vicinity of the urban area, and use the total station to locate and make up the survey. The position error of the supplementary measurement feature points relative to the surrounding obvious feature points is not more than 0.8 mm in the flat and hilly areas and not more than 65438±0.2mm in the mountainous areas, which meets the specified requirements.

2. 1.6 adjustment, decoration and edge connection

Requirements for front decoration of construction drawings: boundaries at all levels, boundaries of land ownership, boundaries of enclaves and boundaries of agriculture, forests, materials and fields should be clearly drawn in red, and enclaves should be marked with the word "fly" in red; Rivers and waters are painted blue; Land boundary, various linear features, figures, etc. It's obviously black.

Dressing requirements on the back of the construction drawing: border, inflection point of land ownership boundary, number and written record shall be dressed in black.

The joint error of the construction drawing shall not exceed 65438±0.5mm in the flat, 2.0mm in the hills and 3.0mm in the mountains.

After field investigation, the field investigation of Xiyang County 12 townships and 423 administrative villages was completed *** 1952 square kilometers, and the orthographic map of the county 107 and the film map were drawn. More than 36,600 maps were mapped, 332 fields were actually measured, and the land ownership boundaries were filled in.

2.2 Internal treatment

After the field investigation is completed, all the field results will be inspected and accepted by stages, and the problem will be solved by combining internal and external methods.

(1)1:10,000, the displacement of a few standard framed orthographic images, the dislocation and loss of individual framed images, the dislocation of the Tu Tu section of the 1,000-meter grid and the large cross coordinate deviation. The orthophoto map and kilometer grid map have been re-made, which ensures the accuracy of the map.

(2) For the problem of less deduction of cultivated land in sporadic areas, register realistically by carefully looking at the field investigation record form.

(3) The problem of insufficient deduction of rural road surveying and mapping is made up by external personnel through careful inspection.

(4) Because the transferred personnel have different understanding of land classification, the same land type has different clear drawings, such as river beaches, grasslands, shrubs, etc. , should be unified in time.

(5) If there are any unclosed points, leakage points, disconnected rivers and roads, and no edges and corners between drawings after site cleaning, centralized solutions will be given.

(6) If the content of the real map is not uniform, it shall be verified on the spot again; If the border agreement is not standardized or sealed, it should be re-standardized and sealed.

(7) Rivers, roads and boundaries are inconsistent with the requirements of field painting and indoor work, and the indoor work shall negotiate with the field personnel according to the actual situation.

2.3 Database construction

Firstly, vectorization is carried out with GeoScan, then editing is carried out under Arc/Info, and then drawing inspection is carried out with AutoCad. If there is no run or drop, enter the library item connection, and make a big splicing after inspection. Finally, transfer to MapGis to establish a land use database. After the acceptance is correct, use "Aidi Land Use System" to draw maps and tables.

2.3. 1 process

Collection of Papers on Land Resources Monitoring and Investigation Project [2]

2.3.2 Operation method

(1) data preprocessing. Scrape off all the tape before scanning the original. Scanning adopts scanner to scan frame by frame, scan resolution 300 lines. When scanning, ensure the clarity of the original data to the maximum extent, and spray the picture immediately after scanning to check whether there is scanning deformation. Before vectorization, check whether patches are closed and whether adjacent maps have boundaries. , and extract no patch number and land type number from the adjacent map, and mark the names and codes of each administrative region to the working map for storage. Because the boundary line on the original image is red, the scanned image is not clear. After redrawing the situation with a pencil, scan it again.

(2) Data acquisition and processing. First, vectorize the map. GeoScan software is used to orient the digital raster map. When the orientation accuracy meets the requirements, the data shall be collected by elements according to the map scale, and the accuracy meets the requirements of the design book. In strict accordance with the "county (city) level land use status database construction data acquisition and hierarchical coding regulations" for hierarchical coding. In order to ensure mathematical accuracy, all lines are required to be centered and strictly checked. On this basis, the vectorized data is transferred to Arc/Info, and the strict topological relationship between lines and surfaces is established. With the help of graphic editing software Arc/Info, the vector data of the map sheet is edited and edged, and the relationship between the elements is handled correctly, reasonably and in line with the requirements. At the same time, the * * * lines in linear features are processed, and the common * * * edges are copied to another layer. The data of Arc/Info are transferred to AutoCad, coded according to different codes, assigned different colors, and painted with sulfuric acid paper drawings to check with the original drawings.

(3) Add library items and edges under (3) Arc/Information. Create a unified attribute structure for each layer, and input patch number, land type number, ownership code, enclave code, etc. One by one. Enter line code, line ownership code, line width, etc. line by line. Enter the ownership code and ownership name by jurisdiction.

(4) Edge stitching and attribute item checking. The technical director shall check all welding conditions. When jointing, not only graphics jointing, but also attributes jointing. Attribute items are checked by two people.

(5) The Grand Masek in the gallery under 5)Arc/Info. All the pictures of 107 are spliced together, and the patch and boundary layer are merged, and then separated after inspection, so as to ensure the uniformity and rigor of the data, and at the same time, the patch and boundary layer are inspected again. After everything is normal, separate the flying layer from the general pattern layer.

(6) Input attribute data with FoxPro. When establishing the graphic library, FoxPro software is used to input the data in the record table, such as slope, soil thickness, ownership nature and so on. At the same time, enter the sporadic feature library.

(7) Establish a land use database based on MapGis. Firstly, the Arc/Info gallery is linked with the FoxPro attribute database, and the survey map index and data dictionary are established by using the "Aidi" land use system, and finally the land use database is established.

(8) Trial operation of database management system. Through the established database, various area summary tables, land statistical account books, land statistical account books, etc. It's all calculated and printed, and the standard framing map and township map are also sprayed.

(9) Each picture has been carefully checked and accepted by the quality inspection department. The qualified rate reaches 100%, and the accuracy meets the requirements of the design book.

2.4 Problem handling in homework

The vector data of all elements are edited in the software environment of Arc/Info. When adjusting the fields, the boundaries are clearly marked in red. After scanning, the image with boundary is not clear, so redraw it. Redraw and rescan the boundary with 2B pencil to make the scanned image as clear as possible; For the unreasonable treatment of the relationship between rivers, roads, boundaries and points in the field surveying and mapping data, the indoor industry should check and deal with them according to the situation. The vector data of the modified 1 ∶ 1000 digital block map and digital image map are checked by superposition, and the line drawing position, attribute accuracy, graphic scanning and data acquisition accuracy all meet the requirements of the design book.

After field investigation, indoor processing and database construction, all the results of land use investigation have been completed.

3 quality control

In the quality control of the results, the inspection method of combining staged self-inspection, roving inspection and inviting experts for technical guidance is adopted, total quality management is implemented, quality monitoring is strengthened, problems in the investigation are solved in time, and the quality of the results is ensured.

3. 1 Strict accuracy of basic data

Only when the basic information is reliable can the survey results be scientific and accurate. Therefore, we should start with the preparation of investigation technology for quality control.

Firstly, the data management system of land use map is established, and the DOM and digital line drawing of land use in the whole county 107 are made to ensure the accuracy and reliability of the investigation basis. The goal of this work is to produce digital orthophoto maps and frame vector element data that meet the requirements of database construction by using existing aerial photographs and conventional operation methods. The technical design is: the digital orthophoto map adopts the method of digital photogrammetry; Through simulation, analytical mapping and scanning vectorization editing, the acquisition of mapping frame vector elements is achieved.

Digital orthophoto map is based on the internal and external orientation elements of the photo (23cm× 23cm, scale 1∶35000) and the ground digital elevation model, and the digital aerial image (monochrome/color) is subjected to digital differential correction to obtain its orthophoto map, and then the image mosaic and contour cutting are carried out to generate map image layer data, which is compounded with map contour modification, kilometer grid and place name annotation data. In order to ensure the accuracy, the digital elevation model is combined with vector data for inspection. That is, after the digital orthographic image and digital line drawing are made, the two images are nested together and about 20 obvious feature points are selected. The calculation error is not more than 5m in general areas and 7.5m in extremely cold areas (it can be relaxed to10m in some places). If the calculation result meets the above tolerance, it can be edited. Otherwise, they should be returned to their respective production processes for inspection.

Digital line drawing (frame vector element data) is the vector data of basic elements on the existing topographic map, which preserves the spatial relationship and related attribute information of each element. Due to the needs of this project, only the elements in the Provisions on Classification and Coding of Data Collection for Land Use Database Construction at County (City) Level are selected. The basic contents include: survey control points, fences, contour lines, topographic points, traffic and ancillary facilities, water systems and ancillary facilities, and boundaries. In the process of drawing data lines, the following quality control methods are adopted: first, check whether the various parameter settings in the vectorization process are reasonable, display vector data and raster images on the screen, check whether the corresponding digital elements are missing, check whether there are short burrs, check whether there are gross errors in elevation assignment, and check whether the drawn contour lines are reasonable. Second, check whether the coordinate values and points in the outline are correct, check whether the coordinate conversion error meets the accuracy requirements, check the correctness of each data layer, check whether the topological relationship of each layer is correct, check whether there is unreasonable adhesion or knot between elements, check whether each attribute is correct, whether the name and definition of the attribute item meet the requirements, whether the attribute value is out of range, and whether the value of each attribute item is correct. Third, check whether the linear elements are strictly consistent with the outline of Tu Tu, whether all adjacent map elements have boundaries, whether the boundary error is within the specified value, and whether the attribute values of the boundary elements are consistent. Fourth, check whether the legend book is complete and correct. The fifth is to check whether all kinds of data, graphics and files are complete, and whether the media and specifications for storing data meet the specified requirements.

3.2 Self-inspection and self-inspection to solve the field problems in the "bud" state.

The field investigation results are an important part of the project results, which are directly related to the scientific reliability of the final results and directly affect the quality of the basic land use maps and data update results. Therefore, in the process of field work, they adopted the methods of patrol inspection, key spot check and centralized correction to ensure the quality of all survey results before building the database.

The problems found in the field investigation are as follows: (1) the scattered land types in the map are incomplete, and some scattered land types such as large scarps, small wasteland, cemetery and water-damaged land are omitted in the cultivated land map; There are many omissions in rural roads with a width greater than 2 meters; The contents in the field investigation record form are incomplete, mainly omitting the terrain slope; The same patch has different quantities, and individual patches are not closed; Some ground features are marked directly on the map (aerial photograph) by visual evaluation or interpretation without using flat-panel instruments or total stations, which does not meet the specified requirements.

In view of the above problems, the improvement methods are as follows: First, the village-by-village survey of the original land base map (or aerial photograph) is carried out to check whether the administrative boundaries and ownership boundaries are consistent and correct. If any inconsistency is found, find the reason for the change again, carefully check and verify the ownership boundary and agreement, and further confirm. Then, from the first map to the last map, from surveying and mapping to the record table, one by one in the whole village. Check whether the plot division is reasonable, whether the boundary is accurate, whether the plot is closed, whether the land type is determined properly, and whether the number on the map is correct; Check whether the contents on the form are complete and correct, and whether they are consistent with the drawings. Also check whether the linear features such as roads and rivers are registered correctly and whether there are any omissions; Whether the scattered land types in the map are fully registered; Whether the expression of enclave is clear; Whether the drawings are connected correctly, etc. In the process of inspection, problems should be dealt with in time, mistakes should be corrected in time, and omissions should be made up in time. Through inspection, the outstanding problems in field surveying and mapping, such as incomplete records of sporadic land types, omission of linear elements, incomplete table contents and inconsistent maps, have been completely solved. The second is to survey new features to ensure the accuracy of surveying and mapping. For the new features extending from the county seat, the total station or flat instrument should be used for supplementary survey, and for the new features with more reference objects and easy positioning, the simple supplementary survey method can also be used for positioning. However, make-up survey must be done carefully, with complete survey records, and the accuracy of make-up survey should meet the specified requirements, that is, the median error of obvious characteristic points around the make-up survey point on the map should not exceed 0.8 mm, and the mountain area should not exceed1.2mm. Third, measure the ridge coefficient according to regulations.

The adoption of the above-mentioned multi-channel and multi-type comprehensive field survey ensures the quality of the whole field survey results and lays a solid foundation for the next field database construction.

3.3 Check at different levels to ensure the accuracy of database construction.

In the construction of the database, we should check it step by step and strictly control it. Several measures have been taken: first, a special map inspector has been appointed. Second, after vectorization, spray the sulfuric acid paper map for the first time. If it is correct, transfer it to Arc/Info for edge connection and storage. Three, after joining, the technical director will check all the joining conditions one by one, and the contents of the library items will be checked by two people, and the mistakes will be corrected in time. The project team will assign special personnel to splice the picture of 107 into a picture and transmit it to MapGis system. Fourth, after the construction of the library is completed, it will be handed over to the quality inspection department of the hospital for inspection.

In the whole process of database construction, we adhere to the operation system of two-level inspection (operation team and branch) and one-level acceptance (quality inspection department of the institute) to ensure the accuracy of database construction results and meet the requirements of the regulations.

4 Conclusion theory

In the survey of map updating of land use status in Xiyang county, the method adopted is more advanced than the previous survey method. First, the technical route adopted in the investigation is correct, and the orthophoto images and data with high degree of digitization applied at the national and provincial levels are adopted. Therefore, the whole investigation is based on science and reliability. This technical method is more scientific and reliable than the previous aerial photogrammetry. In the past, there were only images, but no data information. This time, there are double images and data as a guarantee. Secondly, the establishment of the database overcomes the deviation of manual operation in the past. Not only the geographical elements are based on digital line drawing, but also the area data is automatically generated, which ensures the consistency of maps, tables and numbers. Third, the data collection and results data are all processed and stored by computer, which provides a modern management system for the next step of land use information inquiry, change and management.