Geographical information system (GIS) has been defined by several authors; it has been defined as “a system for capturing, storing, checking, integrating, manipulating, analysing and displaying data which are spatially referenced to the Earth”. As a list of tools for collecting, storing, retrieving at will, transforming and displaying spatial data from a real world for a particular set of purposes. It has also been described as a computer system that can hold and use data for describing places on Earth surface. The topic of GIS is dynamic and its definitions are likely to change quickly as technology and application changes. In this article, GIS is defined as a software package used to input, store, manage, transform and analyses data to produce an output data. It works from an application area and cannot function in isolation. It consists of computer hardware, application software and the persons to operate the system.

A well designed GIS system is able to provide quick and easy access to large volume of data that would be impracticable to do with other means, update data easily, model data and assess alternatives, link or merge one data with another, outputs maps, graphs, address and statistical information and search for specific features in an area. Infact the application of GIS is endless and is used for a great variety of applications, ranging from commerce and business, utilities modelling, environmental managements, defence agencies, socio-economic governments. GIS can answer questions such as; what is the best landfill site, what is the population of vulnerable people in a particular area, what is the type of soil present in an unmapped area, which type of soil would be highly vulnerable to soil erosion during flooding. Finding proper answers to these questions require the manipulation of spatially referenced or geographical data.

GIS model real world on a computer in the same way as the maps represent the world on a paper. The information they both convey are the same but GIS offer more flexibility and easy access than the paper maps. With GIS you can store huge amount of information about features represented on maps on a computer and with a single click on the computer, you can access all the information about the feature.

In GIS, all geographical phenomena are represented in two dimensions by three entity types, namely: points, lines and area and with two additional spatial entities: network and surface. Network and surface are extension of the concept of lines and areas. These five entities also known as spatial objects are used to model real world features in GIS.