An Introduction to GIS
Dateline: 08/03/97This is the story of the fictitious River City and how GIS became an important tool for the city government. GIS is also known as Geographic Information Systems and is being used by a variety of public and private agencies to store and manipulate data about specific locations in a certain area.
With the urging of city staff, the River City Council decided to implement a GIS to keep track of utilities and other city infrastructure. The newly established GIS Division uses a GIS program installed on the city's computers to keep track of all of this data.
They begin by digitizing a "base map" of the city. This base map is a basic map of the city with known boundaries and landmarks so the grid system used by the computer can be accurate and based on the actual location on the earth's surface. Digitizing is a tedious process where a GIS technician uses a device like a mouse with a hole in it and cross-hairs for accuracy when digitizing. The digitizing is done on a specialized table which receives the commands and inputs the data to the computer.
The GIS Division then collects extensive data about the location of all of the fire hydrants, utility poles, property lines, schools, etc. throughout the city. The data can come from maps or from listings of locations along with their coordinates. If the crew has a map of all of the fire hydrants in the city, they gently tape the map to the special table and digitize that data from the map to the computer program.
The data about fire hydrants goes into a separate "layer" of the map. Eventually, all sorts of points (such as fire hydrants and light fixtures), lines (water mains, and streets), and areas (properties, parks, and buildings) are added to the city computers and compose hundreds of individual layers of data. A map of the entire city showing every water main, street, property line, light fixture, and bicycle rack could be produced by GIS but this would probably be too much data to be readable or useful.
The ability of GIS to produce maps on demand using a few layers of pertinent data is valuable. GIS can also manipulate the information and show the city some trouble spots. The GIS Division is asked by the fire chief to produce a map showing residential structures more than 300 feet from a fire hydrant and more than a mile from a fire station. This map is easy for the GIS team to produce since this data is stored in the computer and it just takes a few commands to produce a map for the chief showing these critical areas of the city.
There are a myriad of uses for GIS and in future weeks we'll take a look at some of the technical aspects of this exciting new area!
For more information, read my interview with a GIS specialist for a city government.
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