GIS Data Standards

The backbone of any geographic information system is data.  Three basic types of data are utilized in GIS - map data, attribute data, and image data.

Map data shows the location and shape of geographic features, and the three types of map data are points, lines, and polygons.  Attribute data is the descriptive (tabular or spreadsheet) data that GIS links to map features.  Existing Excel spreadsheets and Access databases are the most common sources of attribute data.  The final type of GIS data, image data, consists of scanned maps, aerial photos, and similar images. 

The quality, compatibility, and uniformity of GIS data is of utmost importance.  Placing quality data into GIS results in good analyses and good mapping, but using bad data results in poor mapping and poor analyses.  In order to improve the County's ability to provide GIS information and products in a more efficient and effective manner, the GIS Work Group has developed the following data format standards for use in the County's GIS.  In summary, these standards are:

Projection = Maryland State Plane
Horizontal datum = North American Datum 1983 (NAD 83)
Units of measurement = meters
Vertical datum = North American Vertical Datum 1988 (NAVD 88)