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| | An Introduction To Geographical Information Systems (GIS) |
 | | This comes about because each set is collected according to a unique set of criteria, partly dependent on the nature of the variables themselves, and partly on the purpose for which they were originally collected. |
 | | For example, air quality and traffic count data are collected and usually reported as point data, land use is reported as regions, election votes are counted by regions, but census data is collected by points (households) and reported by region (enumeration areas, tracts, etc.) due to confidentiality requirements. |
 | | Trying to reconcile two sets of data collected over different tessellations, such as census tracts and postal codes, is another very difficult task, and a complex one for either a GIS or a human to perform. |
| www.badpets.net /IntroGIS/index.html (6707 words) |
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