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Corrected Data Problems

Production of statewide DEMs over the past 15 years went through several technology changes at the U.S. Geological Survey. Early technology (now called Level 1) had the potential to produce "banded" or "mottled" data. Potential problem areas were found in southeastern Minnesota, Otter Tail County, the Chippewa National Forest and a few other small areas. Newer production technology (called Level 2) has been used in the last few years and does not produce these problems.

The image below shows portions of two west-central Minnesota counties, Otter Tail and Wadena. Digital elevation model data for Otter Tail County, on the left hand side, was created by using Level 1 technology and exhibits the mottled problem. The image on the right shows Wadena County data that was created using Level 2 technology. 

DEM Mottled example

LMIC, with the help of the Minnesota Department of Natural Resources, USGS and BRW, Inc., compiled a map of 569 known Level 1 DEMs. Users who have old DEMs should check the header record for Level 1 or 2 reference.

Conversion from Level 1 to Level 2 is now complete for the entire state (note:  USGS is investigating whether three quads are still Level 1:  Town Line Lake, Grand Portage and Grand Portage OE N). USGS redid the Level 1 quads outside the Twin Cities metropolitan area using matching funds from the Legislative Commission on Minnesota Resources, the DNR, the Minnesota Department of Transportation and LMIC. Eighty-eight remaining Level 1 quads in the metro area were redone by DNR. See map of USGS and DNR Level 2 quads.

The files corrected by USGS are distributed by USGS and have been incorporated into derivative products distributed by LMIC and DNR. The files corrected by DNR are contained only in the derivative products distributed by LMIC and DNR.

Page last updated 04/04/2001

Technical problems? Contact: demography.helpline@state.mn.us