It might seem obvious, but before working with GIS data, it must be in digital format. Almost all the elements on the Earth’s surface can be encoded so that a computer can understand them, and, depending on the type of information, one data model or another can be used. What is not so obvious is how to represent the real world in a digital medium (ESRI, 2010).
Despite the heterogeneity of geographic information, there are two basic approaches to simplify and model space, so that it can be stored and manipulated in a computer system, giving rise to two data models: the vector model, usually used to treat discrete geographic phenomena (communications routes, urban fabric, plant cover, etc.), and the raster model, which is generally used to represent continuous phenomena. Both systems are complementary and coexist within GIS, although each of them is more or less appropriate for studying a specific type of information (Del Bosque González at al. 2012).
2.1. Vector model
The vector data model is based on the assumption that the Earth’s surface is composed of discrete objects such as trees, rivers, lagoons, etc. (ESRI, 2010). In this model, there are no fundamental units that divide the collected area, but, rather, the variability and characteristics of this area are collected by means of geometric entities. For each geometric entity the characteristics are constant. The form of these entities is explicitly codified, because it models the geographic space through a series of primitive geometrics containing the most outstanding elements of that space. These primitives are of three types: points, lines and polygons (Olaya, 2014).
2.2. Raster model
The raster structure is based on a matrix of cells represented in rows and columns. Each cell can store information about a given variable (precipitation, temperature, relative humidity, solar radiation, radiance, reflectivity, etc.). The raster model does not explicitly collect the coordinates of each cell, but, rather, the values of each cell. It is not necessary to accompany these values with a specific spatial location, since they refer to a particular element of the mesh, which represents a fixed and regular structure. But it is necessary to place this grid in space so that the coordinates of each cell can be calculated (Olaya, 2014).
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