About this map:

This map uses several distinct geospatial datasets to portray the land surface of the Northern Guam Lens Aquifer (NGLA). Included are the fundamental type of terrain (limestone vs. volcanic), principal geologic faults, closed-contour depressions, and the extent of impervious surfaces. Together, these elements control the recharge of the NGLA. The data sources for GIS files used in this map are indicated on other maps in this atlas that separately showcase the individual elements used in this combination map.