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About geocoding
Geocoding is the process of assigning a location, usually in the form of coordinate values (points), to an address by comparing the descriptive location elements in the address to those present in the reference material. Addresses come in many forms, ranging from the common address format of a house number followed by the street name and succeeding information to other location descriptions, such as postal zone or census tract. An address includes any type of information that distinguishes a place.
From simple data analysis to business and customer management to distribution techniques, there is a wide range of applications for which geocoding can be used. With geocoded addresses, you can spatially display the address locations and recognize patterns within the information. This can be done by looking at the information or using some of the analysis tools available with ArcGIS. You can also display your address information based on certain parameters, allowing you to further analyze the information.
Your first step when you want to find something on a map is to have the right map. Your map must have enough detail of the area to pinpoint the location for which you are searching.
It is no different when geocoding in ArcGIS. The layers that you use for creating an address locator, known as reference data, need to have details of the specific point you want to find. When looking for addresses, the primary reference data usually consists of a street network, but a parcel map can also be used.
Geocoding workflow
There are several steps, known as the geocoding workflow, that should be followed for successful geocoding. See the following illustration and sections that discuss each step:
Building or obtaining reference data
Initially, the geocoding process requires the following types of information:
- Reference data for creating an address locator
- Address data for matching
Reference data refers to a geographic information system (GIS) feature class containing the address attributes you want to search. For example, when searching for house number addresses, the reference data must contain the street names, house number ranges, or address attributes of the specific parcels. In assessing if the reference data that you have will work for your geocoding process, there are a few points to consider based on the extent and resolution of the data.
The reference data needs to cover the same area that you want to geocode. For example, if you are attempting to geocode cities across the entire continental United States, reference data that only presents features in the western states will not perform the task. Each address that you want to geocode must be present on your reference data. This leads to the second property of the reference data, the resolution.
Beyond determining if the data has a spatial coverage that includes all the features you want to geocode, you must also consider if the reference data has information at the detail that you want to search. If you want to geocode individual addresses, your reference data must have information at this granularity. If your reference data only contains street names—not address ranges for each street segment—you will be unable to pinpoint the exact location along that street where the address is located.
Determining address locator style
Address data refers to the individual or group of addresses you plan to geocode. Address data also needs to comply with certain formats. The specific requirements of the address data are based on the elements of the address locator style that you intend to use. In general terms, the address data needs to contain the applicable elements used in matching an address to a feature and must be in an acceptable format.
To correctly geocode, it is important to understand the variety of address locator styles and select the one that best matches your address and reference data.
Building an address locator
Once an address locator style has been selected and reference data has been prepared for that style, you are ready to build an address locator.
An address locator contains a snapshot of address attributes and indexes provided from the reference data, and a set of properties specific to the selected address style. After an address locator is built, addresses can be matched against the address locator. The reference data will be disconnected from the address locator. If the reference data is updated, you can rebuild the address locator to refresh the information. For more information, see How to rebuild an address locator and How to create address locators.
Locating addresses
ArcGIS provides two methods for locating addresses, one for finding individual addresses and one for finding locations for a table of addresses, commonly referred to as batch geocoding. There are several basic steps to locating addresses. This process includes standardizing the input address, finding candidate locations, assigning match scores to the locations, and narrowing down the best candidate. For more information, see How to standardize an address, How to geocode a single address and How to geocode a table of addresses.
Publishing, maintaining, or customizing your address locator
Once you have created an address locator, there are several optional tasks that you can perform. These include the sharing or publishing of the address locator, maintaining the reference data and related address locator, and customizing the address locator. The following outlines these optional tasks:
- Publishing—There is a wide range of methods to distribute an address locator, such as sharing the locator over a local network, reproducing an address locator and the related files onto a compact disc or into a compressed data file, and producing a geocoding Web service.
- Maintaining—When you initially create your address locator, the address locator contains a snapshot of the reference data at the time of creation. However, like most data files, your reference data might require frequent updates. The addition of streets to the feature class, changing street names or zone properties, or improving the accuracy of the geometry of the features all justify modification to the geocoding reference data. When these changes are made to the reference data, you can rebuild the address locator to reflect these changes. If you decide not to rebuild the address locator, geocoding continues to function with the existing locator. It produces geocoding results based on the state of the reference information when the locator was created.
- Customizing—There are a number of methods that can be used to modify your search. You can create an additional address locator, modify the existing one, or create a customized address locator style.
See Also:
Location library overviewHow to create address locators
How to standardize an address
How to geocode a single address
How to geocode a table of addresses
How to rebuild an address locator
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