In this Guide, we have touched on the surface of the vast subject of GIS. We have used a GIS software to illustrate the concepts and to show how one GIS does the job. You will notice that most of what you have learned from this Guide will apply to others because most GIS on the market are based on similar principles. There are, however, some notable differences among them.

User interface. Most of the systems are menu driven, but the window and menu layouts would be quite different from one GIS to another. Moreover, the same operation could be called by different names.

Data types and operations supported. Geographic features are represented by geometric primitives such as points, lines, and polygons in the GIS. Other types that could be found in GIS are text, spot height, sounding, contour, and image. You can tell the number of types available by the commands supported by the software. For example, the presence of a contour-add command normally means that there is a contour type.

A GIS supporting more of these primitives is more flexible in that real world features have direct representations in the database. For instance, if a GIS does not support the contour type, then an ordinary line would have to be used instead. Because a contour is a line associated with an elevation, it contains more information than an ordinary line.

The data types supported by a system are a reflection of its dominant applications. Systems mainly used for map production would have more geometrically-defined primitives such as circles, ellipses, curve-fitting lines, and curve-binding text. Systems used mainly for spatial analysis would support more raster types and topological primitives such as nodes and arcs.

Number of databases used. The GIS we have used, as well as a number of others on the market, employs two databases to store data - one for system-defined data and the other for user-defined data. Some other GIS use only one database.

There are advantages and disadvantages for both schemes. The reason for using two databases is because traditional database management systems (DBMS) are not entirely suitable for managing spatial data. That has forced some GIS vendors to develop their own data management modules for spatial data and incorporate an off-the-shelf relational DBMS to handle non-spatial data. In this way, a two-database system is supposed to give the user the best of both worlds. With data for the geographic features separated into two databases, GIS developers are faced with the challenge of hiding this separation from the users. This is not an easy task, and you probably have noticed the awkwardness this can produce as you used this GIS.
GIS using one database, and hence one data management module for both spatial and non-spatial data, are faced with another challenge, which is to get around the deficiencies of traditional DBMS in handling spatial data.

One of the deficiencies is in the way data are organized. Because relational DBMS are mainly designed for business applications and are not optimized for multi-dimensional data, the use of them for spatial data involves a certain amount of storage and processing overheads. As a result, GIS using one database tend to be slower and consume more storage space. However, developers of traditional DBMS have recognized this problem and some of them are taking steps to correct the situation. Oracle, a major relational DBMS vendor, has recently developed a multi-dimensional version called Oracle-MD.

Learning the operation of one GIS provides you with the experience to make the learning of another easier. The knowledge of one GIS becomes a reference with which to compare other systems. But in order to make sense of the similarities and differences, you must have a good grasp of the concepts.

One way to learn concepts is to read the many books on GIS now available. We have provided a selected list of them here. There are many magazines, professional journals, and newsletters related to GIS and computer. Some of these are free for your asking if you qualify. Attending short courses, workshops, and conferences on GIS will put you in contact with the latest developments. An excellent source of information is the Internet if you have access to it and the time to browse through the large collection of GIS-related sites. A list of some of the useful sites are included at the end of this chapter.

GIS is a dynamic, multi-disciplinary, and exciting field. We hope you will continue to be curious and explore the many possibilities it offers.