Introduction to Mapping and GIS Systems

What is a GIS System?

Computer mapping and geographic information systems (GIS) store and manage geometric representations of geographic features. This may include roads, cities, census tracts, neighborhoods, rivers, canyons, forests. These same GIS systems can also store attributes of these features, permitting spatial analysis of variables that cannot be easily visualized with tables and lists.

Why Use GIS Systems?

The major benefit of using GIS system is the ability to communicate spatial information in presentation-quality maps for analysis and decisions. Maps can be understood more easily than tables and lists (although these fill needs as well).

For example, in a typical city planning office the information about land parcels is traditionally stored in a fragmented way: data files, microfilm, file cabinets, computer tapes. Physical parcel maps are stored in map racks, zoning designations in file cabinets, assessed values in another file, and building regulations in code books. With a GIS system, all the information can be stored in a single place and queried as needed.

How Are the Maps Created?

GIS systems create maps in one or more layers, with each layer representing a specific set of data. One layer, for example, might show census tract boundaries, another neighborhood boundaries. A third layer might show streets, and a fourth layer might show school locations as points, with different symbols and/or colors representing the types of schools, emergency preparedness, cost/student, or other variable. The census tract boundaries are stored as polygons, the streets as lines, and in the school layer the information is stored as points. The polygons, lines, and point locations are all defined by latitude and longitudinal coordinates. A key question, then, is how would one get the latitude and longitude coordinates of the polygons, lines, and points?

The information for census tracts and streets is available f rom often supplied as TIGER files from the U.S. Census Bureau and were created by the government for the 1990 census. These have been updated and corrrected since then and are sold commercially.
Schools and other variable locations can generally be placed using (Global Positioning System) GPS units. These are small units, about the size of cell phones, which are carried to the site and used to query the satellite system. This gives you the actual latitude and longitude where you are standing, which is then entered the database for the layer. On some cases, you can connect the GPS units to a laptop and update the database electronically.
A third method is to purchase layers from local city departments that are already using GIS tools. For example, in Portland the 911 emergency center has mapping software with a neighborhood level and a street level that they updated and more accurate than the commercial layers. This is used with the fire trucks, police cars, and ambulances (which all have GPS units) to manage emergency response effectively. METRO also has this available and you can even purchase thelayers from them. You can often obtain a copy of these layers free or at low cost and use them (sometimes with conversion) with your own mapping program.

Another method is to use a geocoder program with a mapping program. The geocoder reads an address in a database, converts it to latitude and longitudinal coordinates, and then maps the location based on the address. This assumes an accurate street file with its decoder, which in almost any city changes often. For example, if you have database of churches with their addresses, a geocoder can read the file and determine the latitude and longitude of each church and convert the address to a point on a layer.

Most of the maps on this system are created with the programs from Environmental Systems Research Institute. We can create maps using ArcView from the same company. We have street files (with geocoding support) for the entire United States, and can them do area maps for any city. We also have census data information for mapping with some leve of update for the entire United States. We can also map custom data. We can create wall maps, page maps (8 1/2 X 11), or web site maps.