arc gis期末复习考点第八章.doc

Chapter 8 Review Questions 1. Explain the difference between location errors and topological errors. Location errors such as missing polygons or distorted lines relate to the geometric inaccuracies of spatial features, whereas topological errors such as dangling lines and unclosed polygons relate to the logical inconsistencies between spatial features. 2. What are the primary data sources for digitizing? Global positioning systems (GPS) and remote sensing imagery provide the primary data sources for digitizing. These data sources can bypass printed maps and the practice of various methods of map generalization. 3. A digitized map from a secondary data source such as a USGS quadrangle map is subject to more location errors than a primary data source. Why? A secondary data source such as a USGS quadrangle map is subject to more location errors because the map has undergone simplification, generalization, and other practices during the mapmaking process. 4. Although the U.S. National Map Accuracy Standard adopted in 1947 is still printed on USGS quadrangle maps, the standard is not really applicable to GIS data. Why? A GIS uses digital spatial data, which can be easily manipulated and output to any scale. The U.S. National Map Accuracy Standard, on the other hand, is scale dependent. 5. According to the new National Standard for Spatial Data Accuracy, a geospatial data producer is encouraged to report a RMS statistic associated with a data set. In general terms, how does one interpret and use the RMS statistic? One can first multiply the RMS by 1.7308 to get the NSSDA (National Standard for Spatial Data Accuracy) statistic. This statistic represents the standard error of the mean at the 95 percent confidence level. In other words, one can be sure that, 95 percent of the time, the accuracy of a point or a line is within the NSSDA statistic. 6. Suppose a point location is recorded as (575729.0, 5228382) in data set 1 and (575729.64, 5228382.11) in data set 2. Which da