Developing a GIS at the Illinois Department of Revenue

The Illinois Department of Revenue (DOR) collects taxes for both the State of Illinois and units of local government. In Fiscal Year 1992, the Department collected $14.5 billion in taxes including $12.1 billion in State taxes and $2.4 billion in local taxes. Taxes collected by the Department account for 73 percent of general fund receipts for the State. There are more than 6,600 taxing districts in Illinois.

Since the allocation of State tax revenue for State services, such as school funding, depends heavily upon the taxes collected by the Department, the Governor's Office, the Illinois General Assembly, and private sector groups are very interested in how much revenue is being collected and the process being used to allocate the funds at the local level. Responding to these requests has been difficult in the past, except for large geographic areas.

The common thread throughout DOR data is geography: taxing districts, income, sales, replacement and property tax data, legislative districts, Chicago wards, enterprise zones, municipal boundaries, demographic data, and so forth, can all be located geographically on the face of the earth. Because of this, GIS technology can be used to link these various tax data sets allowing much more effective analysis. Understanding this, DOR has formulated the goal "to develop and maintain a geographic information system that would enable the Department to give accurate and expeditious statistical information regarding income tax, sales tax, replacement tax, and property tax as it relates to a geographical area or location."

GIS Solutions, Inc., was selected to assist the Department in developing a GIS that would meet this goal. Tasks include

• The development of a seamless State-wide coverage of all 6,600+ taxing districts, Congressional and State legislative districts, and Chicago wards in Illinois
• Development of a statewide block level (291,000+ blocks) coverage of demographic data using the 1990 STF1-B data from the U.S. Census Bureau
• Geocode 5,000,000+ income tax filers to street address or ZIP+4 centroid
• Overlaying taxing district, census geography, and legislative coverages with the geocoded residential data (point data representing street address location); perform point-in-polygon geoprocessing and tag taxing district, census geography, and legislative codes to individual address records. After geoprocessing, the 5 million records will have the income tax filer's name (for confidentiality purposes), address, city, ZIP+4, and the county, township, incorporated place, census tract, blockgroup, block, school district, junior college district, park district, legislative district, etc., in which that person lives.
• Geocode over 250,000 business tax filers and overlay taxing district, census geography, and legislative coverages with the geocoded business data (sales tax and business registration); perform point-in-polygon geoprocessing and tag taxing district, census geography, legislative codes, etc., to individual address records. The data fields are the same as those listed above for the geocoded residential data.
• Develop applications within ArcView 2 for different divisions within the Department. Applications might include the income tax/property tax trade-off (who wins, who loses, under various tax policy scenarios?); how homestead exemptions affect property tax revenue; tracking and evaluating property sales compared to assessed value; or sales tax generated by business type and taxing district (Where is sales tax revenue increasing? Why? What are the impacts?).
• Integrate GIS database development efforts with the Department's mainframe tax revenue database.

Tim Johnson
GIS Solutions, Inc.
2375 W. Monroe, Suite 303
Springfield, IL 62704
Telephone: 217-546-3635
Fax: 217-546-3839

Robert Lindquist

Mike Maroon

Charllie Fisher

Ron Hagaman