| Description | Spatial | Attributes |
The layer represents all 5 Foor Contours for Prince George's County, Maryland.
Topographic coverage is derived from the digital elevation data taken April, 1993. Index contours, intermediate contours are presented and index contours are appropriately labeled. The countywide topography was interpolated, using the WILD Contour Interpolation Program, from digital elevation data that was stereo-photogrammetrically compiled using geodetic control and 1:14,400 scale aerial photography taken in April, 1993. Topographic contour lines will be developed at five foot intervals using WILD's Contour Interpolation Program (CIP). The CIP will automatically generate contour lines from points obtained through stereo-compilation. Spot elevations along with index, intermediate, index depression, and intermediate depression contour lines will be delineated. Figure 1A-D gives a generalized version of the capture of spot elevations, the building of a digital elevation model, and the interpolation of the various contour line types. Where contour lines disappear under buildings, bridges, culverts, or into dense vegetation, hidden contours will be created to maintain contour connectivity. Hidden line contours will be snapped to the appropriate visible line contours in all instances. Snapping lines means there will be no overshoots, undershoots, or unconnected linework. Index contours will be compiled at every fifth contour. The index contours will be graphically labeled approximately every 6 to 12 inches (every 1200 to 2400 feet at map scale) as measured along the contour line to be labeled. All index contours will be labeled with their elevation given in full feet. All index contours will be graphically labeled at least once per line crossing a sheet model. This labeling will not be done in a regular pattern and, where possible, will be in diagonal stacks and will read uphill. It will be necessary to identify eight different types of lines within a linetype attribute item. Table 1 identifies the coding to be used for each linetype. The elevations for all contour lines will be stored in a three position integer item called ELEVATION. Intermediate contours will represent the four topographic lines between index contours. Intermediate contour lines will not be graphically labeled but will have a linetype attribute coded according to the designated codes and will have an appropriate elevation attribute associated with each intermediate contour line. A depression contour is a contour which closes within the mapping limits, or which obviously closes outside the stereomodel limits, where the area inside the contour is lower in elevation than the contour where the depression starts. There are two types of depression contours: index and intermediate. Index depression contours will be graphically labeled in full feet according to the same rules applied to index contours. Intermediate depression contours will not be graphically labeled. Hidden line attributes will be as specified in the code table and depression contour elevations will be stored in a three-position item called ELEVATION. NOTES: ELEVATION and LAB-SEG values are added items. The ELEVATION item stores the three digit elevation value, LAB-SEG is used to denote hidden contour lines (lines under buildings, bridges, etc.), and FTR-CODE is used to differentiate index and intermediate contour line types. Layer was created by ASI, Inc.