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Application of Orthophoto Maps and Digital Elevation Model


1. Classified forest map
          In the beginning, the forest boundaries were defined from government policies. These maps were manually drawn on the topographic maps, 1:50,000 scale, following the river or topography. 

Figure 1. Classified forest boundaries in topographic maps (1:50,000)

          After MOAC’s project, by using orthophoto maps, classified forest boundaries have been transfered from topographic map,1:50,000 scale, to orthophoto map, 1:4,000 scale. Because of the different scale and coordinate system, reshaping in GIS software was done by GIS staff and verified with field survey.
Figure 2. Classified forest boundaries in Orthophoto maps (1:4,000)


Checking classified forest areas online
Figure 3. Checking classified forest areas online

          Office of Survey and Mapping Technology is providing classified forest boundaries checking method via the internet. Thai people can roughly check if their land is in the classified forest boundaries or not.


2. Soil map

Figure 4. Aerial photo interpretation method for soil mapping

          In the beginning, topographic maps and aerial photo interpretation with soil survey and soil classification were used to identify and delineate soil units as shown in Figure 3.

Figure 5. 3-D model for soil collecting plan

          Soil survey and mapping currently apply orthophoto maps with Digital Elevation Model (DEM) and contour lines with GIS software to create a 3-D model (Fig. 4) for fieldwork planning. 

Figure 6. Analysis soil data with GIS software 

          Soil data were analyzed by using slope class (from DEM), Orthophoto maps, geology maps, hill shade and DEM with GIS Software for creating draft soil maps (Fig. 5).

Figure 7. Cross section created from Digital Elevation Model (DEM)
          Create cross section (Fig. 6) by using a digital elevation model for soil surveyors to collect soil samples from field work. After field work, soil samples are analysis for physical and chemical properties in the LDD laboratory. Then soil properties are recorded to soil geo-database. Finally, soil maps, 25,000 scale, (Fig. 7) are created by using orthophoto maps as base maps.

Figure 8. Soil maps, 1:25,000 scale, with orthophoto maps as base maps



3. Land use map

      3.1 Land use / Land cover maps
          Land use maps in the first period of LDD were created by using aerial photo interpretation. After satellite images were available, the image classification became the standard method.
Figure 9. Aerial photos in 1976 and satellite images

          After LDD has orthophoto maps, land use maps could be created by using orthophoto maps, by comparing with satellite images together with field work examination.

Figure10. Present land use map

       3.2 Land use change maps
          By comparing between orthophoto maps and satellite images, changes in land use can be detected and finally land use change maps are produced.
Figure 11. Khonkaen land use change maps in 2008 and 2010

       3.3 Land use planning
          Land use planning maps are one of the products that can be analyzed by using slope class maps (extracted from MOAC’s DEM) together with topographic maps, soil maps, and present land use maps, with socioeconomic data and relevant policies.

Figure 12. Land use planning map


4. Erosion hazards maps

Orthophoto maps
          - Field work planning

Figure 13. Orthophoto maps and Digital Elevation Model 3-D view

          By using orthophoto maps and digital elevation model, 3-D view can be created for overview of the study areas. Field work planning can be performed without having to go to the areas and thus saving substantial costs to the project. 

Figure 14. Points for collecting data in field work



Digital Elevation Model (DEM)

          Extract watershed boundary

Figure 15. Flow direction (a), flow accumulation (b), stream ordering (c) and watershed boundary (d)

          DEM can extract hydro parameters such as flow direction that shows where the water is flowing to, the flow accumulation of the water that was accumulated, the stream order, and finally that the watershed boundary became well defined.

          - Reduce shadow from the satellite images

Figure 16. Landsat TM image before (a) and after (b) using topographic normalization technique

          Topography itself can cause the problem in land use / land cover classification tasks. The shadow effect can cause the distortion when classifying via remote sensing software. Digital Elevation Model (DEM) can reduce the shadow from satellite images by using topography analysis technique such as topographic normalization that uses DEM to analysis the terrain.

Figure 17. Land cover classification after using topographic normalization


          - Extract erosion model’s parameters
                    1. Rain map

Figure 18. Rain map

                              Using height from DEM, as related to the amount of rainfall, to create a rain map for using as a model parameter.

                    2. Soil detachment by runoff

                              For calculating soil detachment by runoff, the slope indicates how steep the terrain is.

                    3. Transport capacity

                              For calculating transport capacity, slope is calculated as a parameter that determines how far the soil particles can be taken by water.



5. Other government offices outside the Land Development Department (LDD)
          - Ministry of Transportation

Figure 19. Transportation planning map

          - Ministry of Natural Resources and Environment

Figure 20. Land use classification map


          - Department of Public Works and Town and Country Planning 

Figure 21. Urban planning mapping


          - Department of Land

Figure 22. Land parcels map

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