The Universal Transverse Mercator (UTM) grid is an X-Y coordinate system used as a reference on medium- to small-scale maps for representing the three-dimensional curved surface of the earth on a 2-D plane (e.g. a map or computer screen). In this grid, the world is divided into 60 north-south zones, each covering a strip 6° wide in longitude. These zones are numbered consecutively beginning with Zone 1, between 180° and 174° west longitude, and progressing eastward to Zone 60, between 174° and 180° east longitude. Thus, the conterminous 48 States are covered by 10 zones, from Zone 10 on the west coast through Zone 19 in New England. In each zone, coordinates are measured north and east in meters. (One meter equals 39.37 inches, or slightly more than 1 yard.) The northing values are measured continuously from zero at the Equator, in a northerly direction. Southerly values are similarly measured from the Equator, south. A central meridian through the middle of each 6° zone is assigned a "false" easting value of 500,000 meters. Grid values to the west of this central meridian are less than 500,000; to the east, more than 500,000.
MassGIS provides two datalayers which represent this referencing system for the parts of the two Zones (18 and 19) that cover Massachusetts:
- UTMGRID_POLY - a polygon/line layer that can be plotted on a map as a coordinate reference
- UTMPT_PT - a point layer that represents the nodes (line intersections) of the UTMGRID_POLY layer
MassGIS staff produced UTMGRID_POLY using the ARC/INFO command GENERATE. Because two Zones cross Massachusetts and meet at the 72-degrees line of longitude (west of Worcester), each was generated separately, converted to the Mass. Stateplane Mainland coordinate system, and then joined in Arc with MAPJOIN. Consequently, along the "seam" of the two zones the grid blocks have varying sizes and shapes. (Traditionally, map series that use the UTM system, i.e. USGS Topographic Maps, are tiled so that no two zones appear in the same map sheet, thus avoiding such geometric inconsistency.) MassGIS then made the point coverage by using the ARC/INFO command NODEPOINT, in which each node of the grid was converted into a point in UTMPT_PT. All coverages were converted to ArcSDE geodatabase layers.
The polygon attribute table for UTMGRID_POLY contains the following item:
18 => to the west of 72-degrees Longitude
19 => to the east of 72-degrees Longitude
MassGIS is maintaining these datalayers. For additional resources on the UTM coordinate system, visit the following Web site:
|Date published:||May 1, 1996|
|Last updated:||May 1, 1996|