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MIT 11 520 - Geocoding addresses

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IN THIS CHAPTER411Geocoding addresses15 Managing geocoding servicesin ArcMap Controlling the geocodingprocess Finding an address Geocoding a table of addresses Rematching a geocoded featureclassA feature is an object that has geometry. In most cases, this geometry iscaptured by digitizing or scanning paper maps. In many cases, however,geographic data exists that indirectly captures geometry by describinglocations such as street addresses, city names, or even telephone numbers.While humans understand what these descriptions mean and how they relateto locations on the earths surface, computers do not. In order to displaythese locations on a map and perform analyses with them, a computer mustbe given geometric representations (such as point features) of these loca-tions.Geocoding (also commonly known as address matching) is the process ofcreating geometric representations for descriptions of locations. A geocodingservice defines a process for converting alphanumeric descriptions oflocations into geometric shapes.You can use geocoding services in ArcMap to find individual addresses andto geocode tables of addresses. You can also review and rematch the featureclasses and shapefiles that you create by geocoding tables of addresses.In order to geocode in ArcMap, you must first define geocoding services.For information on creating geocoding services, see Using ArcCatalog.Ch15.p65 12/06/2000, 1:30 PM 411412 USING ARCMAPManaginggeocodingservices inArcMapIn ArcMap, you can findaddresses or geocode tables ofaddresses using geocodingservices. Your ArcMap documentcan contain any number ofgeocoding services. You can usethe Geocoding Services Managerto manage the set of geocodingservices contained in an ArcMapdocument.For information on creatinggeocoding services, see UsingArcCatalog.Adding a geocodingservice to an ArcMapdocument1. Click the Tools menu, point toGeocoding, then clickGeocoding Services Man-ager.2. Click Add.3. Browse for the geocodingservice that you want to addto the ArcMap document andclick Add.4. Click Close.1243Ch15.p65 12/06/2000, 1:30 PM412GEOCODING ADDRESSES 413Removing a geocodingservice from an ArcMapdocument1. Click the Tools menu, point toGeocoding, then clickGeocoding Services Man-ager.2. Click the geocoding servicethat you want to remove fromthe ArcMap document, thenclick Remove.3. Click Close.123Ch15.p65 12/06/2000, 1:31 PM413414 USING ARCMAPControlling the geocoding processThe geocoding processOnce you have added a geocoding service to an ArcMap docu-ment, you can begin geocoding addresses with it. However,understanding how a geocoding service matches addresses andhow modifying a geocoding services settings affects this processcan help you improve both the performance and accuracy of yourgeocoding.Geocoding services use a specific set of steps to find a match foran address. First, the geocoding service standardizes the address.Second, the geocoding service searches the geocoding referencedata to find potential candidates. Next, each potential candidateis assigned a score based on how closely it matches the address.Finally, the address is matched to the candidate with the bestscore.When a geocoding service standardizes an address, it dissects theaddress into its address components. For example, the address4Dundas St. E. has four address components: the streetnumber, 4; the street name, Dundas; the street type, St.;and the street direction, E. Each style of geocoding servicestandardizes an address into a different set of address compo-nents.If your geocoding service uses a place name alias table, itsearches this table for entries that match the address you aretrying to geocode to determine if the address is actually a placename alias. If one is found, it substitutes the address in the placename alias table for the place name that you are trying to locateand standardizes this address.Once it has standardized the address, the geocoding servicesearches the reference data to find features with address compo-nents that are similar to the components of the standardizedaddress. Each style of geocoding service bases this search on adifferent set of address components. The geocoding service usesits spelling sensitivity setting for some address components, suchas street name, to determine how closely the address componentsof a feature must match the address components of the addressyou are geocoding. If the geocoding service uses an alternatestreet name table, then it also searches this table to find potentialcandidates.Once the geocoding service has generated a set of potentialcandidates, it scores each potential candidate in order to deter-mine how closely each potential candidate matches the addressthat you are geocoding. Each potential candidate is assigned ascore from 0 to 100. Each address component is used to generatethis score. The score for each potential candidate will be lower ifaddress components are misspelled (for example, the street nameis misspelled), incorrect (for example, the street number of theaddress does not fall within the address range for the candidate),or missing (for example, the street direction is specified in theA geocoding service standardizes an address into a number of addresscomponents.4 DUNDAS ST. E.Street numberStreet nameStreet typeStreet directionThe geocoding service searches the reference data for features withaddress components that are similar to the components of thestandardized address.Ch15.p65 12/06/2000, 1:31 PM414GEOCODING ADDRESSES 415The geocoding service scores each potential candidate using all of theaddress components. A set of match candidates is generated based onthe geocoding service’s minimum candidate score setting.The Geocoding Options dialog box allows you to modify the settings of ageocoding service.address but not in the potential candidate). Once each potentialcandidate is scored, the geocoding service generates a set ofmatch candidates. The geocoding service determines whichpotential candidates are match candidates using its minimumcandidate score setting.Finally, the geocoding service finds the match candidates with thehighest match score. If the score of the match candidate with thebest match score exceeds the geocoding services minimummatch score setting, then the geocoding service matches theaddress to that match candidate.Geocoding service settingsGeocoding services have a number of settings that allow you tocontrol the geocoding process. These


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