Geocoding Addresses in ArcGIS

What is Geocoding?

If you have addresses that you would like to put on a map, or you would like to use your map to find addresses for locations the process to do this in ArcGIS is called address geocoding. While an address allows you to easily find a location when you are walking or driving, a computer has to do more background work to do the same thing.

You will need:

1. Access to ArcGIS software. 2. Reference data. Reference data is the base data that contains information on all the

addresses in your area of interest. 3. Your address data.

How does it work?

When you geocode a table of addresses, you use your reference data to create an address locator to create point features that represent the locations of the addresses.

Addresses have some specific characteristics. An address contains certain address elements and is presented in a range of formats. When geocoding your addresses, the address is interpreted and and compared to the address locator.

Four Steps to Address Geocoding

There are four steps to geocoding your data:

Choose or Create the Reference Data

Your first step when you want to find something on a map is to have the right map. 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. There is no way you will find your way to 380 New York Street in Redlands, California, if you only have a map of Canada. Also, you won't be able to pinpoint the address very well if your map only shows highways and major cities. When you use a map it must have enough detail of the area to pinpoint the location for which you are searching. It is no different for the computer 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. Your first step is to locate GIS data that contains a street network of your area of interest and detailed address information in the associated table. The software searches against this data to find the addresses you are interested in.

The reference data may contain some common address elements that can be used for geocoding including:

• Left house number range (a low number and a high number of the address range for the left side of the street) such as 100, 198

• Right house number range (a low number and a high number of the address range for the right side of the street) such as 101, 199

• Prefix direction (a direction that precedes the street name) such as the W in W. Redlands Blvd

• Prefix type (a street type that precedes the street name) such as Ave in Avenue B • Street name • Street type (a street type that follows the street name) such as St in New York St • Suffix direction (a direction that follows the street name) such as the W in Bridge St. W • Zone (additional information used to resolve ambiguity between addresses by identifying

a region in which the address is located), as in a ZIP Code or city name

Your reference data must:

1. Cover the same area as you want to geocode. 2. Contain the level of detail that you want to search. 3. Contain sufficient address information of a similar type to the data your addresses that you

want to map.

For Address Geocoding in Ontario, the Route Logistics Ontario file from DMTI (ON_rte.shp) is the recommended file to use.

Determining Address Locator style: An Address Locator defines which reference data which will be used to search for addresses, which elements of the reference data are going to be searched against, and what format the address data should appear in. ArcGIS Desktop comes with several predefined address locator styles that you can use to create address locators. An address style includes which elements of the address are present (street name, number, direction etc.) and which will be used in locating your addresses. Each address locator style has specific requirements for the reference data that it can use to match addresses as well as the format of address data being geocoded. The address locator also sets the parameters of the search – what constitutes a matched address, tolerance for spelling errors etc…

Choosing the right address locator style depends on knowing what type of reference data you have and in what format your addresses will be.

You will need to:

1. Acquire and open your reference data and make note of what address information is included and the format. You will set the address locator style when you create your address locator.

2. Open your address data and make note of what address information is included and the format. You will later need to format your address data to conform to the style you select.

Addresses are represented in a wide range of formats. A common address format used consists of the following series of address elements: house number; prefix direction, prefix type, street name; street type, suffix direction; and zone information such as city, state, and ZIP Code.

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While various addresses differ to some degree, some things remain consistent. Each address consists of several address elements, presented in a particular address format recognized by those in the region.

Learn more about the methods for address data presentation. http://webhelp.esri.com/arcgisdesktop/9.3/index.cfm?TopicName=Preparing_reference_and_address_data 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. Learn more about predefined and commonly used address locator styles. http://webhelp.esri.com/arcgisdesktop/9.3/index.cfm?TopicName=Commonly_used_address_locator_styles

Build 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 may rebuild the address locator to refresh the information. Building an address locator begins in ArcCatalog.

Steps to Geocode a Table of Addresses in ArcGIS

You must have completed the steps listed above to acquire and examine your data and reference data before you can begin this process.

To create or modify any address locator file, you must have write permission to the computer where you create and store the address locators. Creating an address locator in ArcCatalog

1. Open ArcCatelog (click the yellow file cabinet icon in ArcMap). 2. Open a workspace in ArcCatalog. It can be any file folder or a geodatabase. It is

recommended that you create a folder called Address Locators and use that folder. 3. Right-click the workspace, click New, and click Address Locator to display the Create

New Address Locator dialog box

4. Click the address locator style you want to use to create the new address locator and click OK. (If you are geocoding in Ontario and using the On_rte file then select “US Streets” style.)

5. Type a name and description for the new address locator in the Name and Description text boxes.

6. Click the Browse button on the Primary table tab.

7. Navigate to and click the shapefile that the address locator will use as reference data, then click Add.

8. Click the drop-down arrow and click the name of the field that contains the specified address information.

The required address elements appear with a bold field name.

9. Click the Alternate Name table tab if your address locator will use an alternate street name table.

Otherwise, skip to step 12.

10. Click the Browse button, navigate to and click the table the address locator will use as an alternate street name table, then click Add.

11. Click the drop-down arrow and click the name of the column containing the specified alternate street name information. Both the primary table and alternate name table require a Join ID field.

The required alternate street name attributes have field names in bold type.

12. Click Place Name Alias Table if your address locator will use a place name alias table.

Otherwise, skip to step 15.

13. Click the Browse button, navigate to and click the table the address locator will use as a place name alias table, then click Add.

14. Click the drop-down arrow and click the name of the column containing the specified place name alias information. The alias names have to be unique in the place name alias table. An address locator style that supports additional zone fields should be used, and the place name alias table should include the address and zone fields if there are mulitple aliases with the same name but in different zones such as Town Hall for "456 Main Street, Cerritos" and Town Hall for "3546 1st Avenue, Lakewood".

The required address fields for the place name alias have field names in bold type.

15. Click OK.

16. Click OK to create the new address locator.

Edit your address table to conform to your address locator style Your address data will need to match the content and format of your reference data and conform to the parameters laid out in your address locator.

1. Open your address data in Excel. 2. Check that each element of your data, (eg street number, street name, street direction,

street type, city etc. ) are divided into the same columns as in your reference data. 3. Check that your column headings are as indicated in your address locator. 4. Check that you have all the required address elements for each address. 5. Check spelling for each address. 6. Save your file and then close it.

Locate 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.

Finding an Individual Address: 1. Click the Find tool in ArcMap, then click the Addresses tab. 2. Choose the address locator you want to use to find the address from the list.

If the address locator you want to use does not appear in the list, you need to add it to the ArcMap document. Click the Browse button to browse for address locators to add to the document.

3. Type the address components in the text boxes and click Find.

For more information on locating an individual address please see the ESRI help on the topic. http://webhelp.esri.com/arcgisdesktop/9.3/index.cfm?TopicName=Finding_an_individual_address

Getting an address for a location on your map: You can use the Address Inspector tool to click on map and get the address of the location. This process is also called reverse geocoding.

The Address Inspector tool uses an address locator to find the address of a point on map.

1. Add an address locator and the street data to map.

2. The Address Inspector tool on the geocoding toolbar will become enabled if there is at least one address locator added to the map. The tool will use the current address locator from the list as shown in the Address Locator Manager dialog box.

3. Hold down the left mouse button over any street location. An address for the location will be displayed in a tooltip text box.

For more information on getting an address for a location on your map please see the ESRI help on the topic.

http://webhelp.esri.com/arcgisdesktop/9.3/index.cfm?TopicName=Getting_an_address_of_a_location

Geocode a Table of Addresses How to geocode a table of addresses in ArcMap

1. Add the table of address you want to geocode to ArcMap. 2. Click the Tools menu in ArcMap, point to Geocoding, then click Geocode Addresses. 3. Click the address locator you want to use to geocode the table of addresses and click

OK.

This will close the dialog box and open the Geocode Addresses dialog box. If the address locator you want to use does not appear in the list, click Add to browse for the address locator. You can also click the Geocode Addresses button on the Geocoding toolbar to open the Geocode Addresses dialog box.

4. Click the drop-down arrow, then click the table you want to geocode.

If the table does not appear in the drop-down list, click the Browse button to browse for the table.

5. Choose the column name from each drop-down list that contains the specified address information.

The names of the required address attributes are shown in bold type.

6. Click the Browse button and navigate to the location where you want to create the geocoded feature class.

7. Click Save. 8. Choose the Create dynamic feature class related to table option if desired. 9. Click Advanced Geometry Options to specify the geometry settings for the geocoded

feature class. 10. Specify the geometry settings for the geocoded feature class and click OK. 11. Click Geocoding Options and specify the geocoding options that will be used to geocode

the table of addresses, then click OK. 12. Click OK on the Geocode Addresses dialog box to geocode the table. 13. When the matching process is completed, you will see the basic statistics of the result.

You can click Close to finish, or click Rematch to open the Interactive Rematch dialog box to review and rematch the addresses.

Learn more about rematching a geocoded feature class.

After a table of addresses is geocoded, the output feature class will contain a copy of the address fields from the address table that are used for rematching. The names of this set of address fields are prefixed with "ARC_". When an address is modified during rematching, the new address will be saved in these fields. In addition, here are the other fields created in the output feature class for the geocoding results:

• Status—A code indicating whether the address was matched. This attribute has values of "M" for matched addresses, "U" for unmatched addresses, and "T" (tied) for addresses for which there were more than one candidate with the best match score.

• Score—The match score of the candidate to which the address was matched. • Match_type—A code showing how an address was matched. "A" for automatically

matched or rematched. If the geocoded feature classes is rematched using the Interactive Rematch dialog box, you may see other values including "M" for manually matched or unmatched using the Match or Unmatch button. "PP" stands for Pick by Point. The address was matched to the click point using the Pick Address from Map tool in the Interactive Rematch dialog box with ArcMap. And "PA" stands for Pick by Address. That means the address was matched to closest address with the Pick Address from Map tool. You may group the results based on this attribute to show how the addresses were matched or use the grouping to select records for rematching.

• Side—The side of the street to which an address was matched, if the address locator that was used to match the table contains address information for both sides of the street. This attribute has values of "L" for the left side of the street, "R" for the right side of the street, or nothing if the address locator could not determine the side of the street.

• Match_addr—The address that the matched location actually resides based on the information of the matched candidate. For example, an input address "123 Main St N" is matched to a candidate with the suffix direction "NW" and all other components

matched correctly. The Match_addr field will contain "123 Main St NW" as the actual address that was matched.

There are also some optional fields if the Output Fields options were checked in the address locator's property page:

• Pct_along—For address locators that use feature classes with polyline geometry as reference data, the percentage along the matched feature at which the matched address is located.

• Ref_ID—The ObjectID of the matched feature. • Stan_addr—The standardized address. • X—The x-coordinate of the matched address. • Y—The y-coordinate of the matched address.

For more information on Geocoding a table of addresses please see the ESRI help on the topic: http://webhelp.esri.com/arcgisdesktop/9.3/index.cfm?TopicName=Geocoding_a_table_of_addresses.