Wednesday, 1 April 2015

#GIS: AN INTRODUCTORY OVERVIEW PART 2 OF 4

How GIS Works

#GIS is important today because it is able to bring together information from multiple sources so that various types of work can be done. In order to do this though, the data must be tied to a specific location on the #Earth’s surface. #Latitude and #longitude are usually used for this and the locations to be viewed are attached to their points on the #geographic grid.
In order to then do an #analysis, another set of data is layered on top of the first one to show #spatial patterns and relationships. For example, elevation at specific locations can show up in the first layer and then rates of precipitation at various places in the same area can be in the second. Through a GIS analysis patterns about elevation and the amount of precipitation then arise.
Also important to the functionality of GIS is the use of #rasters and #vectors. A raster is any type of digital image, such as an #aerial #photograph. The data itself however is depicted as rows and columns of cells with each cell having a single value. This data is then transferred into GIS for use in making maps and other projects.
A common type of raster data in GIS is called the #Digital #Elevation #Model (#DEM) and is simply a digital representation of #topography or terrain.
A vector is the most common way data is shown in GIS however. In #ESRI’s version of GIS, called #ArcGIS, vectors are referred to as #shapefiles and are made up of points, lines, and polygons. In GIS, a point is the location of a feature on the geographic grid, such as a fire hydrant. A line is used to show linear features like a road or river and a #polygon is a two dimensional feature that shows an area on the earth’s surface such as the property boundaries around a university. Of the three, the points show the least amount of information and the polygons the most.
The #TIN or Triangulated Irregular Network is a common type of vector data that is capable of showing elevation and other such values that change consistently. The values are then connected as lines, forming an irregular network of triangles to represent the land’s surface on a map.
In addition, GIS is capable of translating a raster to a vector in order to make analysis and data processing easier. It does this by creating lines along the raster cells that have the same classification to create the vector system of points, lines, and polygons which make up the features shown on the map.
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