The availability of GPS (Global Positioning System) has been examined in three areas. The first is a fixed point on the roof of a building of the University of Tokyo. The second area is around the Hishikari gold mine, southwestern Japan. The area was selected because topographic maps (1/25, 000) are published. The topography consists of gentle hills. The third area is Yunnan Province, southwestern China, where foreigners are prohibited to use topographic maps. The surveyed area is mostly mountainous. Measured values at the fixed point are scattered within 100m from the true position. The average point is located 30m south from the true position. In the Hishikari area, each GPS value is compared with the coordinates given by a topographic map. The deviation between the GPS value and the coordinates is within 300m. The reason why the deviation is larger than the error at the fixed point is that the coordinates given by a map includes error. In Yunnan, the accuracy was checked by the reproducibility. At many sites, satellites were not found because of steep slopes and high trees. A relatively wide space was located, however, within 300m from each site. When 4 satellites were found in wide areas, values were scattered in a circle with a diameter of 200m. When 4 satellites were found in narrow areas, the diameter was 500m. When only 3 satellites were found, the diameter was 1, 000m. These values are larger than the error of the pacing (less than 10 m for 100m distance). The result suggests that the GPS can provide location data with the accuracy enough to geoscience discussions in regional scales.
