Abstract
Topographic Base Maps (TBMs) are those maps that portray ground relief as the form of contour lines and show planimetric details. Various other maps like geomorphological maps, contour maps, and land use planning maps are derived from topographical maps. In this constantly changing world, the update of TBMs is indispensable. In Nepal, their update and maintenance are done by the Survey Department (SD) as a national mapping agency. This paper presents the history of topographical mapping and the reasons for the lack of updates. Currently, the SD is updating the TBM database using panchromatic and multispectral images from the Zi Yuan-3 (ZY-3) satellite with a resolution of 2.1 and 5.8 m, respectively. The updated methodology includes the orthorectification of images, the pansharpening of images, field data collection, digitization, change detection, and updating, the overlay of vector data and field verification, data quality control, and printing map production. A TBM in the Dang district of Nepal is presented as casework to show the changes in the area and issues faced during the update. Though the present digitizing procedure is time-consuming and labor-intensive, the use of high-resolution imagery has made mapping accurate and has produced high-quality maps. However, audit and automation can be introduced from the experiences of other countries for accurate and frequent updates of the TBM database in Nepal.
Highlights
Topographic base maps (TBMs) are maps that show planimetric details and altimetric details, i.e., the portrayal of relief utilizing contour lines [1]
An up-to-date TBM database is important for Nepal
Current TBMs distributed by the Survey Department (SD) of Nepal were prepared during 1992–2001 AD with the support of the governments of Finland and Japan
Summary
Topographic base maps (TBMs) are maps that show planimetric details and altimetric details, i.e., the portrayal of relief utilizing contour lines [1]. In Nepal, as an NMA, the Survey Department (SD) bears a responsibility to give the updated geo-information of the country to support multi-sector development activities and has a policy that indicates that updating of base maps should be carried out on a 10–20 year cycle using new air-borne or space-borne imagery [3] These updates include gradually accurate topographical information collected with cutting edge technologies, data on altering land cover, enhanced transport networks, increasing developed areas, and other land use. A higher region requires varying altitude and flight types, so aerial flight for a required area is virtually impossible In such a case, only satellite imagery is the best and most cost-efficient, and recent support from the Chinese government and allocated budget from the Nepalese government initiated the first official update of national scale TBMs. Nepal has started to produce many geomatics engineers [15] by starting geomatics engineering programs in different universities, increasing the number of skilled surveys professional and accomplishing more technological advancement to make the update procedure quick.
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