All GIS mapping must be done at a source scale of 1:24,000 or better. This can be accomplished in several ways. The method used must be reported in the attribute table for each layer.
- Points, lines, and areas can be field mapped on paper USGS 7.5’ quads and digitized from the paper maps. This requires a digitizing tablet and an understanding of how to register the paper maps on the tablet with an existing GIS dataset. It may not be an efficient method for most CRU consultants.
- Points, lines, and areas can be field mapped on paper USGS 7.5’ quads or low altitude aerial photographs, then heads-up digitized using a raster image (USGS 7.5 minute DRG or DOQ) of the same quad or photo as background. Any photographic images used as mapping backgrounds must be rectified and orthogonalized, and their scale must be known to be 1:24,000 or better. MnDOT base maps in GIS format can be downloaded from mndot.gov/maps.
- X,y coordinates for points, lines, and boundaries of areas can be recorded in the field using GPS. GPS technology used must have an accuracy of +/- 40 feet or better. These coordinates can then be used to generate an event theme that should be saved and transmitted as a shapefile. UTM coordinates interpolated from USGS topographic sheets are not acceptable as GIS input.
- At a scale of 1:24,000, it is always acceptable to digitize polygons, instead of points or lines, for features exceeding 40 feet in both length and width. However, these features must be clearly represented at a scale of 1:24000. Very small polygons are sometimes more difficult to find on a GIS map than points or lines. The Consultant may determine whether points, lines, or polygons are best for displaying features smaller than 40 acres. All features 40 acres or larger must be digitized as polygons.
- Character values in attribute tables must use the capitalization convention specified for each field and be correctly spelled. Be consistent in how you enter your firm’s name in the Contractor field. For example, do not use “HUDAK AND ABEL” for one project and “HUDAK & ABEL, INC.” on another.
- Be sure that the format of your data values matches the examples given in the tables below. For example, do not use “S.P.” instead of “SP”.
- When reporting site numbers or inventory numbers, be sure that your values exactly match those in the SHPO/OSA database. Do not use “WA-SWC-72” instead of “WA-SWC-072” or “21SH58” instead of “21SH0058”. We have to use these numbers to link our database to SHPO’s and OSA’s.