Define Data Requirements

A geographic database covers a certain area and serves a specific purpose. Some are used to manage forest stands in a country, some to aid geological explorations within a region, and some to help highway construction for a city. The municipality database we have been using supports land use planning, property records, and network analysis for part of the City of Fredericton.

In order to better define the contents of the database, we first consult our potential users and then consolidate their requirements for data into a single design often called a database schema.

The process of developing a database schema for a certain application is called database design, and it is carried out at several levels of detail. A high-level design for our municipality database reveals that we need the following types of geographic features:

o Properties each corresponding to a land parcel.

o Street centre lines for network analysis.

o Trees, street lights, utility poles, and fire hydrants.

o Contours for flood analysis.

As for attributes, we decided that they are required only for land parcels. Again, input from the potential users will be sought to create the attribute list as shown in Appendix C.

Such a design has to be implemented with a GIS. But before we can do this, we have to identify the sources of data because the scale, projection, and other characteristics could affect the implementation plan.

Identify Sources of Data

Data for a geographic database can be obtained in various ways. You can gather data from ground surveys, digitize them from existing maps, or transfer them from other systems. A review of the data collection methods is given in the chapter on Data and Its Collection.

For the municipality database, we transferred most of the data from a provincial properties database. The contour lines were interpolated from a digital elevation model. The floor plan of the school was converted from a file produced by AutoCAD, a Computer-Aided Design (CAD) software. We have also obtained digital data from the National Topographic Data Base (NTDB) maintained by Geomatics Canada.