Surplus map interpretation for the landform change and its unique characteristics

Abstract

In this paper, a method for making a surplus map for interpreting landform changes and a field application example of the map are shown, and the characteristics of the map were discussed. The surplus map is a layer tinting map in which surplus obtained by dividing the elevation change value by the denominator of a certain integer is classed by different colors. In this map, the degree and direction of the elevation change can be identified by the striped pattern, so that the unique landform change is easy to interpret. The surplus from the small denominator can indicate the landform change with a small amplitude, and it from the large denominator can indicate the landform change with a large amplitude. Since the ratio of the area where the striped pattern is recognized in the map changes depending on the denominator, it is necessary to select an appropriate denominator that makes it easy to interpret interesting landform change.

In the 2016 Kumamoto earthquake, small landform changes related to fault displacement occurred in many places in Mashiki Town. Elevation changes due to this earthquake could be calculated using lidar data. Small landform changes could not be recognized in the elevation change map, but they were easy to interpreted in the surplus map with a denominator of 18.

The surplus map can realistically indicate the extent and change values for the area where elevation change is smaller than the height accuracy of the laser measurement. This characteristic is based on the condition that the digital terrain model matches the actual landform well and that the elevation change indicated by the surplus map is relative. Therefore, the surplus map can indicate the distribution of elevation and elevation change according to the landform scale by the striped pattern, and makes it easy to interpret the landform and landform changes. It is important that this research has clarified various characteristics of the surplus map and discussed their inducing backgrounds from the viewpoint of geomorphology and cartography.