DNR Coordinate Reference System
The coordinate reference system in use at the DNR is the Wisconsin Transverse Mercator coordinate system of 1983 based on the 1991 adjustment to the North American Datum of 1983. This is known as WTM83, NAD83 (1991). An alternate term for this coordinate reference system, "WTM83/91", is being phased out of use in DNR GIS documentation. The term "WTM83, NAD83 (1991)" is preferred as it is more consistent with terminology used for other Wisconsin statewide, regional, and local coordinate reference systems.
For the purposes of data integration, there are significant advantages in making all agency geographic data available for internal use in a single statewide coordinate reference system. This approach is intended to better enable DNR GIS users to integrate agency data sets. It also enables integration of statewide vector data with the accumulating raster data, including digital orthophotos, digital raster graphics, and WISCLAND land cover data.
A coordinate reference system is defined by its coordinate system (and zone, where appropriate) and its geodetic system (datum and datum adjustment). To create a single coordinate referencing system for agency use, the DNR has chosen the WTM83 coordinate system and the NAD83 (1991) datum.
WTM83 is a UTM-based coordinate system, modified to cover the state of Wisconsin in a single zone. WTM83 represents a redefinition of the Wisconsin Transverse Mercator coordinate system for the North American Datum of 1983. The WTM83 coordinate system may be used with any adjustment of the North American Datum of 1983, including the upcoming NAD83 (NSRS2007) adjustment. However, the Wisconsin DNR recommends use of the NAD83 (1991) adjustment as an agency standard.
NAD83 (1991) refers to the geodetic datum adjustment based on Wisconsin's high accuracy reference network (HARN). Wisconsin's HARN was the first established for the nation and was originally known as the High Precision Geodetic Network (HPGN).
The coordinate reference system is cited as: WTM83, NAD83 (1991).
Defining parameters for the WTM83 coordinate system are identified below.
Grid Coordinate System Name: WTM83 (Wisconsin Transverse Mercator of 1983)
Map Projection Name: Transverse Mercator
Longitude of Central Meridian: -90 degrees West
Scale Factor at Central Meridian: 0.9996
Latitude of Projection Origin: 0 degrees
False Easting: 520,000
False Northing: -4,480,000
A projection file with the WTM83, NAD83 (1991) coordinate reference system parameters for use with ArcGIS software, is available for download from the DNR external FTP site using your web browser.