3.3.2 The attribute table

One of the points that distinguishes GIS from graphics tools is that layers are not only composed of geometric elements (points, lines or polygons: concept developed below). Each layer is also associated with what is called an attribute table This table contains information (attributes) on each element of the layer. For a layer listing cities for example, these attributes can be: name, postal code, population, city type, etc. This information is stored in a table, composed of rows and columns. Each row corresponds to a geometric element and each column corresponds to an attribute. The number of rows and columns therefore depends on the number of elements in the layer and the number of associated attributes. As in an Excel table, the columns and the information they contain can be of different types: number, text, date, etc. On the illustration below, we can see the data layer on 4 communes in Brittany, as well as its attribute table with different columns which are as many attributes (id, nom_comm, code_insee, code_dept).

The attribute table