Past and Present Practices of Topographic Base Map Database Update in Nepal

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.

CHALLENGES AND OPPORTUNITIES: ONE STOP PROCESSING OF AUTOMATIC LARGE-SCALE BASE MAP PRODUCTION USING AIRBORNE LIDAR DATA WITHIN GIS ENVIRONMENT. CASE STUDY: MAKASSAR CITY, INDONESIA

LiDAR data acquisition is recognized as one of the fastest solutions to provide basis data for large-scale topographical base maps worldwide. Automatic LiDAR processing is believed one possible scheme to accelerate the large-scale topographic base map provision by the Geospatial Information Agency in Indonesia. As a progressive advanced technology, Geographic Information System (GIS) open possibilities to deal with geospatial data automatic processing and analyses. Considering further needs of spatial data sharing and integration, the one stop processing of LiDAR data in a GIS environment is considered a powerful and efficient approach for the base map provision. The quality of the automated topographic base map is assessed and analysed based on its completeness, correctness, quality, and the confusion matrix.

I coloured a map: Darwin's attempts at geological mapping in 1831

In his autobiography describing his geology of 1831 Darwin wrote, “on my return to Shropshire I coloured a map of parts around Shrewsbury.” There are four extant maps in the Cambridge University Library, which fit this description. Two, at a scale of ⅞ inch to 1 mile, are of Anglesey and Llanymynech and are hand-drawn copies of Evan's map of North Wales, and are without geological annotation. The other two of Shrewsbury and Kinnerley have a scale of 1 inch to 1 mile and are copied from Baugh's Map of Shropshire (1808). These contain orange shading to the west of Shrewsbury indicating New Red Sandstone, but make no allowance for drift. The Shrewsbury map includes some attempted stratigraphic boundaries and marks four sites; A, B, C and D. These maps demonstrate Darwin's grasp of geology before his Welsh tour with Sedgwick in August 1831. They show his realisation of the need of a topographic base map, an acquaintance of the conventions of geological mapping in shading and the marking of boundaries. These maps form an early part of Darwin's considerable geological activity in the summer of 1831.