Positional Accuracy: Horizontal accuracy is no worse than + or - 170 ft.
Coverage creation: The DLG files were read from 9-track tapes supplied by the USGS. The Arc/Info DLGARC command was used on all 34 sets of DLG files to create Arc/Info coverages of the 1:100,000 quads. The Arc/Info PROJECT command was used on all 34 map coverages to project coordinates from Albers into the MARIS Transverse Mercator projection to enable viewing and manipulation of statewide files. The Arc/Info CLIP command was used on all of the 26 - 1:100,000 coverages that contain Mississippi's border.
Editing: Using the USGS 1:100,000 quad maps , TIGER county maps,and the Mississippi Department of Transportation county maps as a verification base (hereafter referred to as source maps), each coverage was checked for correct coding and geographic placement. Once the codes were verified, further classification schemes were determined to ease the use of the USGS major and minor codes. For example, each road was
given one of nine values based on the major and minor codes. Separation of the major types of hydrology and roads into a variety of unique coverages
was performed to meet the requirements of multiple applications. The hydrology was separated into 1) polygon water bodies and wide rivers (graphically displayed by two lines), 2) perennial streams, and 3) intermittent streams. The roads were separated into 1) primary roads, 2) secondary roads, and 3) county roads, city streets, and trails. These coverages were checked for coding consistency and corrected using the source maps. The coverages were then joined using the Arc/Info APPEND command to form statewide coverages and checked to ensure non-duplicate lines, consistent coding between 1:100,000 coverages, and edge-matching of arcs.
Enhancements: At the statewide level of spatial organization, all additional attributes such as highway number and polygon water type (e.g.
CLASS = 1 is Islands, CLASS = 5 is the Gulf of Mexico) were added and checked by referencing the source maps. County coverages were created by the Arc/Info CLIP command using the county borders from the 1990 TIGER files. All major and minor codes were retained at the county level. These coverages were again checked with the source maps.
Annotation: Annotation added to the coverages was based on the USGS 1:100,000 paper maps and MS county highway maps. Annotation
was created for the major rivers coverage on a statewide level and the perennial streams on the county level. MARIS created a highway symbol marker set for mapping at various scales. A point coverage is used to access the Federal and State highway shields.