We know that the analytical capabilities of a GIS make use of spatial and non-spatial (attribute) data to answer questions and solve problems that are of spatial relevance. We now make a distinction between analysis (or analytical operations) and analytical models (often referred to as "systems models". In this learning path we will first discuss the analytical models in a more general way, followed by an indepth discussion of analytical operations that can be performed on vector data. Please note that there is also a Learning path focussing on raster analysis and one for network analysis.
A few general characteristics apply to all models. When building a model, you should be aware of these characteristics and the steps in the modelling process.
After this short introduction of system modelling, we will focus on basic analytical functionality in the remaining part of this Learning Path. Analytical functionality can be grouped in the following way: 1. Measurement functions 2. Classification functions 3. Retrieval functions 4. Overlay functions 5. Neighborhood functions This learning path follows this sequence starting with "Measurements".
In the next concept we will zoom in on Vector Measurements. For Raster Measurements refer to the Learning path "Raster Analysis"
In the next topics we will discuss: - Interactive spatial selection - Spatial selection by attribute conditions - Combining attribute conditions - Spatial selection using topological relationships
The next concept zooms in on "Selection by attribute". Also refer to the Learning Path on SQL.
Various forms of topological relationship between spatial objects were discussed in previous Learning paths (See: Topology in 1.3). These relationships can be useful to select features as well. In the next concept you will learn more about selection using topological relationships.
The next group of analytical operations are Reclassification operations. Reclassification can also be performed on Raster data (See the next Learning path).
In the previous concepts, various techniques for measuring and selecting spatial data were discussed. In the next concept we look at techniques for combining two spatial data layers and producing a third layer from them. We will focus on vector overlay operations, raster operators will be discussed in the next learning path.
There are many different vector overlay operators. However, we will restrict ourselves to three examples: "Intersect", "Clip" and "Overwrite". These operators are discussed in the next topic.
In spatial analysis it can be useful to find out the characteristics of the vicinity, here called neighborhood, of a location. After all, many suitability questions, for instance, depend not only on what is at a location, but also on what is near that location. The most common technique within the vector operations is buffer zone generation. Another technique based on geometric distance that will be discussed is Thiessen polygon generation.
The next concept will explain the principles of Buffer generation including the zonated buffer.
Besides Buffer, Thiessen polygons are another vector neighborhood operation that is much used. Thiessen Polygons will be discussed in the next concept.