GIS, Imagery, Mapping

What is GIS?

Learning to read, my youngest daughter looked at her dad proudly as she shouted out the letters on his T-Shirt…“G I S!”. Then she looked at me inquisitively and said “Mommy, G I S?” I responded in the affirmative, “Yes sweetie, G I S!”

So, what is GIS?

This picture which I captured on my return flight to Montserrat, overlooking Davy Hill and Little Bay will help me to explain.

View overlooking Davy Hill and Little Bay, Montserrat

At first glance, buildings, roads, vegetation, hills and the ocean can be seen in my picture. GIS, which stands for Geographic Information System allows you to capture, store, manipulate, analyse, manage and present, this type of geographic data.

The unique aspect about GIS is that it allows you to store additional information, called “attributes”, about each feature. For example, attributes of a road may include its name, type, whether primary or secondary and its length. Similarly, attributes of a building, may include the owner’s name, a category of use, whether it is residential or commercial, the material that the building is made from, for example, wood or concrete, the roof type and also the number of floors.

Attribute data can be obtained from a number of sources or data can be captured specifically for your application. Spatial data can be obtained from satellite images, aerial photographs, scanned maps and similar resources. Essentially, any format of a geographical image with location or co-ordinate points can be used as spatial data.

The combination of spatial and attribute data gives GIS the capability of providing answers to complex questions. It is undeniably, the partnership of these two data types that enables GIS to be such an effective problem solving tool through spatial analysis.

To visualize large amounts of information interactively is one of the most attractive and useful capabilities of GIS. To do this, data is extracted and stored in the form of “layers”.  The image below captures graphically how these layers relate to the real world.

                           Representation of layers in GIS

GIS utilizes two primary data types: vector and raster. Vector data is represented as either points, lines, or polygons. So let’s go back to my picture of Montserrat. In that picture, the location of a particular facility, such as the new location of ZJB Radio in Davy Hill can be captured as a point, other buildings can be represented as polygons, along with the entire settlement area of Davy Hill and the roads can be captured as lines.

Contrastingly, raster data is best suited for information that does not have hard boundaries or locations. So again, let’s revert to the picture which I took. The hills and valleys which you can see are best represented as elevation or terrain modelling surfaces. Raster data is usually used to represent this type of data in a GIS. Data in rasters are viewed as a series of grid cells where each cell has a value representing the feature being observed. 

Unlike, traditional paper maps, GIS is fully interactive. It allows you to add new fields of data,  change the color scheme or form of the map, add text and move symbols around. GIS displays allows you to zoom and pan which offers new perspectives and new insights. These and a host of other capabilities give a user tremendous flexibility and power.

GIS is more than just software. It is a system where trained people and methods are combined with geospatial tools, to enable spatial analysis, manage large datasets, and display information in a graphical form.

GIS Day is celebrated annually, read more in my previous blog: https://www.lavernrogersryan.com/celebrate-gis-day-annually-and-dont-forget-the-cake/.

Lavern Rogers-Ryan is a geospatial consultant specializing in disaster risk management and recovery. She is currently head of the GIS Centre within the Government of Montserrat. Learn more about geospatial services in disasters at www.lavernrogersryan.com.

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