1. Digital Line Graph files from the U.S. Geological Survey (USGS), including data from the base map categories such as transportation, hydrography,hypsography, roads contours, public land survey boundaries and other features. The USGS distributes digital data for that branchs in vector form in a standart format they call a Digital Line Graph 2. The digital format standards published by USGS for exchanging cartographic data files and in which the USGS delivers Digital Line Graph data sets.
