Stated simply geospatial information is information where the location is an important component of understanding the information. It is essential to remember the difference between Information and data, where data is symbolic, in our case digital) representation of Information. In this section, we will focus on Geospatial information while Geospatial data will be covered later. Geospatial information generally falls in one of two categories namely Field-based information and Entity-based information
Field-based information is information relating to a property that is present at all locations and varies continuously through space e.g. elevation, temperature, air pressure noise in Db. This is often called a property field. It can be practically to distinguish between continuous and quasi-continuous property fields, a property such as air temperature varies continuously (smoothly) through space while a property such as the surface of a town or an image has locations for instance at the edge of a building where it varies abruptly, while at has other locations, for instance, a roof where it varies constantly this is called quasi-continuous i.e. partly continuous.
Entity-based information is information that is bound to a physical or conceptual entity e.g. a building, road, municipality school district etc. These entities have one or more properties that have a constant value within the entity i.e the number of 0-5-year-old children in the school district or the height of a building. Entities are typically conceived as instances of an entity-type so a specific building is an instance of the entity type building. All entities of a given entity class carry the same properties. Entities are spatially delimited as points, lines or polygons.
The ontology and world of discourse
It is common to talk about the collection of entity-types and property fields used in a given project as the project’s ontology. The area of interest and the information held by entities and property fields within this area of interest is often called the “world of discourse”. You can think of the “world of discourse” as the environment you wish to describe seen through the lens of the ontology i.e only described in terms defined by the ontology. It is important to understand that the world of discourse can include both tangible and intangible aspects of an environment and that this environment can be both an existing environment, a future planned environment or an entirely fictitious environment. A more detailed discussion of property fields, entities and entity classes can be found in the post “Modelling Spatial Information”