ABSTRACT: There is a growing need to systematically map soil erosion using GIS and related
technologies for speed and accuracy. The soil erosion map in Northeast Thailand was established
with objective of providing the risky areas of soil loss and the methodology for spatial modeling
with universal Soil Loss Equation (USLE) and GIS. The study area, Northeast Thailand, covers an
area of about 170,000 Sq km or 1/3 of the Kingdom area. A set of USLE factors as defined were
studied and reviewed in terms of the values assigned for each of the factors. These factors consist of
rainfall erosivity factor (R-factor), soil erodibility factor (K-factor), slope and slope length factor
(LS-factor), vegetative cover factor (C-factor) and conservation practice factor (P-factor). The
factor layers were collected from a number of existing information and satellite data. Each of the
USLE factor was digitally encoded in a GIS database to establish the factor layers. Simultaneous
overlay operation with the USLE model on the factor layers was digitally performed to produce the
erosion class. The study indicated that the severe erosion class covers an area of about 7.94% of the
total area and is located in the mountain areas where the slope gradient is very high with the
degraded forest. The result provides a spatial distribution of soil erosion and overall insight into
causes of soil erosion resulting from the interaction of the USLE factors spatially and quantitatively.