Digital map coordinates represent the locations of real world entities. As such, differences can exist between the ‘true' and digital database coordinates of those entities. This paper reports on a statistical characterization of positional error in manually-digitized and map-registered point data, the relative contribution of point type and operator to digitization error, and the effects of map media type on the positional uncertainty associated with registration. Manually-digitized point data were collected by four operators from mylar and paper maps. Point locations for a number of different feature types were sampled from United States Geological Survey (USGS) 1:24 000 scale maps. Linear models were used to estimate the variance components due to among-operator, map media, point type and registration effects. The statistical distribution of signed distance deviations for manually-digitized data was leptokurtic relative to a random normal variate. Unsigned deviations averaged 0-054 mm. Squared distance deviations were not different from a Chi-square random variate. Variance components indicate that among-operator differences in positional uncertainty were large and statistically significant, while differences among point type were small and non-significant. Signed distance deviations associated with a first-order affine followed a normal distribution. Unsigned distance deviations associated with a first-order affine transformation averaged 0068 mm, and squared distance deviations were distributed as a Chi-square. Differences in transformation accuracy were not related to type of map media.
|Original language||English (US)|
|Number of pages||14|
|Journal||International Journal of Geographical Information Systems|
|State||Published - Jan 1 1990|