DEM Header Info

Each DEM file contains a header that gives detailed information about the file. You can view this information by selecting "View|DEM Info" option from the menu bar.

Here is an explanation of each of the header items:

Map Name. This item gives a description of the file. It usually contains the name of the quadrangle and some information about its location. If the file has been converted from another format, there may be notes on the conversion here.

Level Code. This information describes the quality of the data in the DEM file. Level 1 represents raw data where only gross blunders have been removed. Level 2 represents data where random errors have been removed and the data has been smoothed for consistency. Level 3 represents data that has been edited to insure positional accuracy relative of the points.

Pattern. This item specifies the pattern of the data. Code 1 represents regular data, Code 2 represents random data.

Ground Ref. This item describes which coordinate system is used to locate the points. Code 0 represents Long/Lat coordinates. Code 1 represents UTM coordinates. Code 2 indicates that State Plane coordinates are being used.

Zone. If the Ground Reference is UTM, this item holds the UTM Zone.

Projection. This item gives UTM projection parameters. Refer to USGS Circular 895-B for further information.

Ground Units. This item represents the units for measurements in the file. Code 0 indicates radians, Code 1 indicates feet, Code 2 indicates meters, and Code 3 represents arc-seconds.

Elevation Units. This item indicates the measurement units used to represent the elevation of the points. Code 1 indicates feet and Code 2 indicates meters.

Poly Sides. This item indicates the number of sides of map. The number is usually four.

Corners. These items give the locations of the each of the corners of the map.

Min, Max Elevation. These items give the value of the highest and lowest point on the map.

Angle. This item shows how the map is rotated relative to geographic coordinates. Normally, this value is zero.

Accuracy. This item specifies the accuracy of the map. A value of 0 indicates that the accuracy is unknown. A value of 1 indicates that accuracy is specified at the end of the file. Refer to USGS Circular 895-B for further information.

Resolution. The three values in this item specify the resolution for the X, Y, and Z portions of the map respectively. For one-degree maps, this value is usually 3 arc-seconds. For 7.5-minute maps, the value is usually 30 meters.

Rows, Cols. This number specifies the number of row and columns in the map. Normally, the row value is set to one, so it is actually the column value that is meaningful.