Land Use Planning Information>Introduction to GIS

Geographic Information Systems
Maps Basics
GIS Basics
Benefits of GIS

Maps Basics

The value and usefulness of maps seems obvious to most people working to provide services to communities. To plan a bus route, school employees may use a map to locate clusters of student homes, road speeds and conditions, and street characteristics curves and corners of streets. Department of Public Works employees use maps to locate, inventory, and manage waterline valves or fire hydrants. Zoning administrators use property description maps to help builders place structures on lots in proper relation to property boundaries.
A typical dictionary definition of the word map says it is a representation of a region of the earth or skies, usually on a flat or "plane" surface. In other words, we select an area of earth's curved surface and represent the features found there as elements drawn on a flat piece of paper or computer monitor. In most cases, we want this representation to depict the location of things and their relationships accurately. For example, a city street map should show that Second Street is between First and Third Streets and at nearly equal distances from both.
To achieve a relatively accurate and reliable representation of things on earth, we use an appropriate scale and coordinate system. The scale provides the relative proportions of things and their relationships. For example, a typical subdivision map using a scale of one-inch equals 100 feet (or 1:1200) will depict a football field as a rectangle with a length of three inches. Coordinate systems are used to provide a clear, mathematical description of where things depicted on the map are actually found on the earth. In general, a coordinate system assigns a pair of numbers to each and every point on the surface that is mapped (three numbers are needed to describe location and elevation). For example, a specific point in your community can be described precisely by two numbers given in degrees of latitude north of the equator and degrees of longitude west of the prime meridian at Greenwich, England. Local mapping in many states is often done using the State Plane Coordinate System, which describes locations in feet or meters, making it easier to calculate distances on the map.

Regardless of the scale and coordinate system used, maps are never completely accurate for a number of reasons. One good reason is that human beings make errors in measurement. Another is that the earth's surface is curved. To depict earth's curved surface on a flat piece of paper, some error must be accepted.

GIS Basics

The vast majority of information maintained by local units of government across the nation relates to the land or some specific place on the land. That is, most government information can be georeferenced. Appraising property involves knowing parcel lines; managing infrastructure involves knowing where utilities like power and sewer lines are located and where they are needed; master plans, zoning ordinances, and other land use plans are informed by the landscape and are described in terms of the landscape.
Anything that can be georeferenced can be fed into a Geographic Information System, or GIS. GIS is a rapidly maturing information technology that links coordinates of geographic location with data about mapped features. By relating map features and their coordinates to records in a database, a GIS permits geographic analysis of database information with the speed made possible by having digital information. This makes it easier to do things like decide where to place a new development in relation to existing infrastructure and without disrupting habitat.
Additionally, a GIS can link data sets together by common locational data. This makes it easier to allow different users to share their data allowing one department to benefit from the work of another. For example, using a GIS you can ask or "query" a database to produce a map of parcels colored according to assessed value, year purchase, or any other field in the database. A GIS operator can quickly sort information about things that are mapped, like parcels, and create new maps to characterize spatial distributions of things, like taxable value.

Benefits of GIS

Information technology experts across the country have encouraged the adoption of GIS by local units of government. In general, maps are easier to create, use, maintain, correct, and re-print in a computer environment. Digital data can be stored, duplicated, transferred far more efficiently than paper records. By linking databases to maps for display and analyses, GIS can also support more effective land use planning, infrastructure planning and management, bus routing, and a whole host of analytical activities by allowing visual pattern recognition. There is a vast difference between seeing data in a table of rows and columns and seeing it presented in the form of a map. The difference is not simply aesthetic, it is conceptual, consider how often we say "I see" and really mean "I understand".
Although the situations vary from one location to another, the list of benefits available to most local units of government that use GIS often include:
  • Reduced time spent on map revisions and re-prints.

  • Easier data management and protection against the catastrophic loss of valuable maps.

  • Easier & more complete analysis of spatial information for land use and infrastructure planning, delivery of services such as police and fire protection, and community development.

  • Improvement in the quality and timeliness of information services exchanged between departments and provided to the community.

  • Improved ability to respond quickly to emergency situations where geographic information and specially formatted products are important.

  • Improved ability to meet the heightened expectations of citizens for more and better information delivered rapidly.
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