User:EKraemer-352P

The GIS accuracy depends upon source data. Land Surveyors have been able to provide high level of positional accuracy utilizing the GPS derived positions, the high-resolution digital terrain and aerial imagery, the powerful computers, Web technology, are changing the quality, utility, and expectations of GIS to serve society on a grand scale, but nevertheless there are other source data that has an impact on the overall GIS accuracy like: paper maps that are not found to be very suitable to achieve the desired accuracy since the aging of maps affects their dimensional.

    Developing a Digital Topographic Data Base for a GIS the topographical maps are the main source of data. Aerial photography and satellite images are extra sources for collecting data. The scale of a map is a very important aspect since the information content depends mainly on the scale of the map. In order to digitize the map, the map has to be checked with the theoretical dimensions, than scanned into a raster format, than the raster data has to be given the theoretical dimension by rubber sheeting/warping.
   Uncertainty is a significant problem in GIS because spatial data tend to be used for purposes for which they were never intended. Some of the maps were made many decades ago and at that time the computer industry was not even in the perspective. Map accuracy is relatively an issue of minor importance in cartography. Maps use a very constrained technology of pen and paper to communicate a view of the world to their users. Cartographers feel little need to communicate information on accuracy, but when the same map is digitized and input into a GIS, the mode of use changes. The new uses extend well beyond the domain for which the original map was intended and designed.
      A quantitative analysis of maps brings accuracy issues into focus. The equipment used to make measurements in GIS is far more precise than the machines of conventional map analysis.  The truth is that all geographical data are inherently inaccurate, and these inaccuracies will propagate through GIS operations in ways that are difficult to predict.

Accuracy Standards for 1:24000 Scales Map

                                  1:24,000 ± 40.00 feet 

This means that when we see a point on a map, its "probable" location is within a +/- 40’ area. Reference list: 1.USGS, National Mapping Program Standards, http://nationalmap.gov/gio/standards 2.United States National Map Accuracy Standards 3.www.fgdc.fgdc.gov/standards/documents/standards/accuracy/chapter3.pdf.