GEOGRAPHIC INFORMATION SYSTEM By WILLIAM T. SUNLEY, Engineer of Local Roads and Streets Credits to: Larry Piche, Local Project Development Engineer.

Geographic Information System (GIS) can easily be defined as a computer system capable of holding and using data describing places on the earth's surface. For over two thousand years, maps have been used to represent information about the earth. Maps have now evolved into sources for a variety of information including jurisdictional boundaries, transportation systems, land ownership, property taxation, utility locations, emergency service response routing, and much more information useful to public and private decision makers. Rapid technological advances in computer hardware and software have fueled an explosion in the development of geographic data useful in providing this information.

A GIS combines the graphic abilities of a computer-aided design system with the information-storing capacity of a database. By combining the two, a GIS enables a user to ask questions of a map and find out detailed information about land use, soil composition, parcel ownership, and accident data. GIS can easily be updated and can conduct a search by multiple categories. For example, it can generate a report on the accidents and severity of the accidents at an intersection or road segment.

The Illinois Department of Transportation (IDOT) has methodically planned GIS implementation over a long time frame. To date, IDOT has generated a computerized roadway network from the 1:63,360 scale county maps. These county maps provided the base to create a series of links and nodes that represent the roadway network. This link/node base encompasses all state, county, township, and non-residential municipal streets. IDOT is currently evaluating methods to incorporate the residential street network. IDOT will undertake an extensive data verification process before making GIS information available to outside agencies.

In 1995, the Illinois Geographic Information Council was created. The council's purpose is to make recommendations to the Governor and General Assembly on the efficient development, use, and funding of geographic information management technology for Illinois' state, regional, local, and academic agencies and institutions. The council will have 18 voting members composed of state agencies and members of the General Assembly, and up to 10 additional voting members representing local, regional, and federal agencies, professional organizations, academic institutions, public utilities, and the private sector.

GIS offers numerous applications for local agencies. Before GIS, public utilities were manually drawn on separate maps. The maps were cumbersome to work with because each map contained limited data forcing the user to flip back and forth between maps to gather the data needed. GIS stores all of this data and is capable of providing only the pertinent data requested. It can be used to manage the growth of new subdivisions around a municipality and analyze the effects of the new subdivision's storm water system on the existing storm water system. It can be used to schedule roadway-maintenance projects based on pavement condition, previous history, and its importance to the highway system. GIS can provide data concerning land use issues, taxation and tax district boundaries, and parcel ownership.

The high cost of creating a Geographic Information System is leading counties, municipalities, townships, utility companies, and others to join forces. This cooperation not only reduces the cost per agency, but it brings together most of the system users enabling the many proposed functions of the system to be defined at an early stage. The benefits of building and maintaining a GIS do not accrue overnight. As a number of state and local governments are discovering, the results are worth it. •

June 1996 / Illinois Municipal Review / Page 5