Some Concepts That Underpin GIS - Introducing Geographic Information Systems with ArcGIS - page 31

Points

Here, for example, is a map and part of a relational database that together describe fire hydrants in a
town. (See Figure 1-13.) Each hydrant has a unique number and is, thus, the key field. Fire hydrants
(each of which has a latitude and longitude specification) correspond one-to-one with the records in the
database.

Let's consider another definition of GIS: From a computer software point of view, a GIS is the marriage of
a (geo)graphical database and an attribute database (frequently a relational database).

Lon

Lat

°
°
°
°

Hydrant Flow Inspected

383 High 1994

Lon Lat

°

888 Low 1989

36 Medium 1998

Points

FIGURE 1-13 Marriage of a point geographic database and a relational database table

Lines

As mentioned earlier, a GIS can store and analyze pseudo-one-dimensional entities such as roads.
Here, each RDB table record would refer to segments of a roadway between intersections. The
attributes might be number of lanes, highway number, street name, pavement type, length, and so on.
See Figure 1-14.

Again: A GIS is the marriage of a (geo)graphical database and an attribute database.

Lines

FIGURE 1-14 Marriage of a line geographic database and a relational database table