Saturday, March 04, 2006

What is GIS

There are a lot of complex definitions about what GIS is. The simplest definition is that GIS is a software that allows to interact with spatial georeferenced data. This means that in theory we can represent almost everything we see each day in a GIS software.

In practice this is much more difficult as it might see. Indeed, modelling spatial information depends most of the cases in the available data and the scale that they can be used to represent some real model.

Generally speaking, only today, major companies and public sectors realized the importance of having georeferenced and structured spatial information as the need of exchange information as become more crucial to help providing good decisions. Nevertheless, there is still a big step to be made when it comes to create a unified information system between major map suppliers. This would allow the exchange of information in real time, without having to follow the constant bureaucracy that makes impracticable a fast take of action when an incident occurs. This could be done with a simple protocol between the several entities.

As Google showed to the common user, GIS can be very useful to provide spatial information that helps us knowing where we are relating to the world. As this information becomes more important to the people, several companies are trying to conquer the market of GIS (phone companies, etc.) and the need of having accurate spatial information as become then even more important.

The only way of representing geographic information, is to provide point coordinates that can relate the spatial information with the world.

To simplify I'll divide the coordinate systems in two major groups (geographic coordinates):
1. Ellipsoidal Coordinate System - Using an ellipsoidal surface, is defined a coordinate system with a latitude (defined relative to the equatorial plane of the ellipsoid), a longitude (defined relative to the meridian) and an ellipsoidal height (measured under a normal to the ellipsoid).
2. Cartographic Coordinate System – When using a projection to define a bidimensional coordinate system.

In order to get more precise coordinates, it is common to use an ellipsoid of reference, positioned in a earth station (local datum), whose natural coordinates are well known.

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