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DLGs - Digital Line Graphs
DLGs consist of several layers of 1:24,000 map scale (vector) data for each USGS defined quad:
- boundaries,
- hydrography,
- vegetative surface cover,
- non-vegetative features,
- roads and trails,
- railroads,
- pipe and trans lines,
- and manmade features.
Large Scale
The large-scale DLG data primarily are derived from USGS 7.5-minute topographic quadrangle maps at 1:24,000 and 1:25,000 scales (1:25,000 and 1:63,360 scales for Alaska).
Intermediate Scale
Intermediate or 100,000-scale DLG data are derived from USGS 1:100,000-scale, 30- by 60-minute quadrangle maps. If these maps are not available, Bureau of Land Management (BLM) planimetric maps at a scale of 1:100,000 are used.
Small Scale
Small or 1:2,000,000-scale DLG data are organized two ways (by section or by State) and contain information on planimetric base categories, including transportation, hydrography, and boundaries for all 50 States. The Section DLG data files are historical files dating between 1973 and 1980 that are organized by sections of the United States (e.g., northeastern States). The State data files are recent files dating between 1990 and 1994 that are organized by State.
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