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Sheet1 Page 1 UNIT 29 - DISCRETE GEOREFERENCING <toc.html#UNIT29> UNIT 29 - DISCRETE GEOREFERENCING # A. INTRODUCTION <#SEC29.1> # B. STREET ADDRESS <#SEC29.2> * Using addresses in GIS <#SEC29.2.1> * Method <#SEC29.2.2> * Example - Addmatch using TIGER <#SEC29.2.3> # C. POSTAL CODE SYSTEMS <#SEC29.3> * US ZIP Codes <#SEC29.3.1> * Canadian Postal Code <#SEC29.3.2> * Problems <#SEC29.3.3> # D. US PUBLIC LAND SURVEY SYSTEM <#SEC29.4> * PLSS References <#SEC29.4.1> # E. GEOLOC GRID <#SEC29.5> * GEOLOC References <#SEC29.5.1> * Precision <#SEC29.5.2> # F. CENSUS SYSTEMS <#SEC29.6> * Converting to georeferences <#SEC29.6.1> # G. ISSUES CONCERNING DISCRETE GEOREFERENCING <#SEC29.7> * Hooks <#SEC29.7.1> * Purpose <#SEC29.7.2> * Standardization <#SEC29.7.3> # REFERENCES <#SEC29.8> # DISCUSSION OR EXAM QUESTIONS <#SEC29.9> # NOTES <#SEC29.10> This lecture concludes the module on geocoding. Several important practical issues are raised here that will be important particularly for those who will be working with economic and demographic databases. UNIT 29 - DISCRETE GEOREFERENCING A. INTRODUCTION <#OUT29.1>
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Sheet1 Page 2 * the georeferencing methods covered so far (latitude- longitude, Cartesian, projections from latitude/longitude to the plane) are continuous o this means that there is no effective limit to precision, as coordinates are measured on continuous scales * will now look at discrete methods - systems of georeferencing for discrete units on the earth's surface * many of these methods are indirect o this means that the method provides a key or index, which can then be used with a table to determine latitude/longitude or coordinates o for example: a Zip code is an indirect georeference + rather than give latitude/longitude for a place directly, it provides a unique number which can be looked up on a map if coordinates are needed * because these methods are indirect, it is important to consider the precision of these systems o precision is related directly to the size of the discrete unit which forms the basis of the georeferencing system * many methods of indirect or discrete georeferencing are in common use o following are 5 of the most common B. STREET ADDRESS <#OUT29.2> * the precision of street addresses as georeferences varies: o is highest for apartments or houses in cities o is lowest for rural addresses or post office box numbers, where the address may indicate only that the place is somewhere in the area served by the post office Using addresses in GIS <#OUT29.2.1> * general approach is to match address to a list of streets (called address matching or "addmatch") o spelling and punctuation variations make this difficult + e.g., Ave. or Avenue, apartment number before or after street number o a failure rate of 10% is regarded as good, 40% is not uncommon. In such cases it is necessary to find the street by hand, which may take as much as 5 minutes per address in large cities Method <#OUT29.2.2> 1. identify the block containing address from table of address ranges in each block o i.e., 551 B St. lies in the block running from 501 to 599
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