Tunisian Association for the Digital Geographic Information
Geographic Information System
Overview of GIS
Geographic Information System (GIS) is a computer based information system used to digitally represent and analyse the geographic features present on the Earth’ surface and the events (non-spatial attributes linked to the geography under study) that taking place on it. The meaning to represent digitally is to convert analog (smooth line) into a digital form.
Every object present on the Earth can be geo-referenced”, is the fundamental key of associating any database to GIS. Here, term ‘database’ is a collection of information about things and their relationship to each other, and ‘geo-referencing’ refers to the location of a layer or coverage in space defined by the co-ordinate referencing system.
Work on GIS began in late 1950s, but first GIS software came only in late 1970s from the lab of the ESRI. Canada was the pioneer in the development of GIS as a result of innovations dating back to early 1960s. Much of the credit for the early development of GIS goes to Roger Tomilson. Evolution of GIS has transformed and revolutionized the ways in which planners, engineers, managers etc. conduct the database management and analysis.
Defining GIS
A GIS is an information system designed to work with data referenced by spatial / geographical coordinates. In other words, GIS is both a database system with specific capabilities for spatially referenced data as well as a set of operations for working with the data. It may also be considered as a higher order map.
GIS technology integrates common database operations such as query and statistical analysis with the unique visualization and geographic analysis benefits offered by maps. These abilities distinguish GIS from other information systems and make it valuable to a wide range of public and private enterprises for explaining events, predicting outcomes, and planning strategies.
A Geographic Information System is a computer based system which is used to digitally reproduce and analyse the feature present on earth surface and the events that takes place on it. In the light of the fact that almost 70% of the data has geographical reference as its denominator, it becomes imperative to underline the importance of a system which can represent the given data geographically.
A typical GIS can be understood by the help of various definitions given below:
- A geographic information system (GIS) is a computer-based tool for mapping and analyzing things that exist and events that happen on Earth
- Burrough in 1986 defined GIS as, “Set of tools for collecting, storing, retrieving at will, transforming and displaying spatial data from the real world for a particular set of purposes”
- Arnoff in 1989 defines GIS as, “a computer based system that provides four sets of capabilities to handle geo-referenced data :
- data input
- data management (data storage and retrieval)
- manipulation and analysis
- data output.
- Hence GIS is looked upon as a tool to assist in decision-making and management of attributes that needs to be analysed spatially.
Answers GIS can give
Till now GIS has been described in two ways:
- Through formal definitions, and
- Through technology’s ability to carry out spatial operations, linking data sets together.
However there is another way to describe GIS by listing the type of questions the technology can (or should be able to) answer. Location, Condition, Trends, patterns, Modelling, Aspatial questions, Spatial questions. There are five type of questions that a sophisticated GIS can answer: Location What is at………….?
The first of these questions seeks to find out what exists at a particular location. A location can be described in many ways, using, for example place name, post code, or geographic reference such as longitude/latitude or x/y.
Condition Where is it………….?
The second question is the converse of the first and requires spatial data to answer. Instead of identifying what exists at a given location, one may wish to find location(s) where certain conditions are satisfied (e.g., an unforested section of at-least 2000 square meters in size, within 100 meters of road, and with soils suitable for supporting buildings)
Trends What has changed since…………..?
The third question might involve both the first two and seeks to find the differences (e.g. in land use or elevation) over time.
Patterns What spatial patterns exists…………..?
This question is more sophisticated. One might ask this question to determine whether landslides are mostly occurring near streams. It might be just as important to know how many anomalies there are that do not fit the pattern and where they are located.
Modelling What if……………..?
What if…” questions are posed to determine what happens, for example, if a new road is added to a network or if a toxic substance seeps into the local ground water supply. Answering this type of question requires both geographic and other information (as well as specific models). GIS permits spatial operation.
Aspatial Questions
What’s the average number of people working with GIS in each location?” is an aspatial question – the answer to which does not require the stored value of latitude and longitude; nor does it describe where the places are in relation with each other.
Spatial Questions
How many people work with GIS in the major centres of Delhi” OR ” Which centres lie within 10 Kms. of each other? “, OR ” What is the shortest route passing through all these centres”. These are spatial questions that can only be answered using latitude and longitude data and other information such as the radius of earth. Geographic Information Systems can answer such questions.
The Three Views of a GIS
A GIS is most often associated with maps. A map, however, is only one of three ways a GIS can be used to work with geographic information. These three ways are:
- The Database View: A GIS is a unique kind of database of the world-a geographic database (geodatabase). It is an “Information System for Geography.” Fundamentally, a GIS is based on a structured database that describes the world in geographic terms.
- The Map View: A GIS is a set of intelligent maps and other views that show features and feature relationships on the earth’s surface. Maps of the underlying geographic information can be constructed and used as “windows into the database” to support queries, analysis, and editing of the information. This is called geovisualization.
- The Model View: A GIS is a set of information transformation tools that derive new geographic datasets from existing datasets. These geoprocessing functions take information from existing datasets, apply analytic functions, and write results into new derived datasets.
Together, these three views are critical parts of an intelligent GIS and are used at varying levels in all GIS applications.
Need of GIS?
GIS is much more than mapping software. Maps are only one of three views of a GIS. When deployed with a clear strategy, GIS is a technology that can change an organization fundamentally and positively.
Modeling Our World
Most computer technology is designed to increase a decision-maker’s access to relevant data. GIS goes beyond mining data to give you the tools to interpret that data, allowing you to see relationships, patterns, or trends intuitively that are not possible to see with traditional charts, graphs, and spreadsheets.
More than that, a GIS lets you model scenarios to test various hypotheses and see outcomes visually to find the outcome that meets the needs of all the stakeholders. For example, a retail manager looking to build a new store can analyze consumer demographics and the locations of competitors in relation to potential locations in a spreadsheet view. GIS lets that manager visualize potential locations on a map along with drive-time analysis, environmental concerns such as wetlands or protected species that might hamper construction, or any number of siting criteria that would be too cumbersome to comprehend otherwise.
