Open map List

Spatial data layer

Introduction

A spatial data layer is either a representation of a continuous or discrete field, or a collection of objects of the same kind. The main principle of data organization applied in a GIS is that of spatial data layers. Usually, the data are organized such that similar elements are in a single data layer (Figure 1). For example, all telephone booth point objects would be in one layer, and all road line objects in another. A data layer contains spatial data, as well as attribute (i.e. thematic) data, which further describes the field or objects in the layer. Attribute data are quite often arranged in tabular form, maintained in some kind of geo-database.

Figure 1: Various objects displayed as area objects in a vector representation. Similar data types are stored in the same single layer (e.g. Buildings). For each different type a new layer is used (b).

 

Explanation

Figure 2: Two different object layers can be overlaid to look for spatial correlations; the result can be used as a separate (object) layer.

Data layers can be laid over each other, inside a GIS package, to study combinations of geographic phenomena. We shall see that a GIS can be used to study the spatial correlation between different phenomena, albeit requiring computations that overlay one data layer with another. This is schematically depicted in Figure 2 for two different object layers. Field layers can also be involved in overlay operations (Figure 3).

Figure 3: Different rasters can be overlaid to look for spatial correlations.

For a more detailed discussion of the functions offered for data management by GISs and database systems, refer to Database Management Systems (DBMS).

 

Learning outcomes

Prior knowledge

Outgoing relations

Incoming relations