Mapping can be a laborious process until you get the right result. Viewing data to analyze and interpret spatial information on a computer is one thing, but printing a map for others to analyze and interpret is quite different. ArcMap makes available a number of tools for map design prior to publication (Hillier, 2011). In general, the simpler a map is, the easier it is to understand. This means avoiding unnecessary content, selecting appropriate colors, selecting the correct text size and prioritizing information according to its relevance. In other words, it is not just a matter of creating a map that is pleasing to the eye, but one that can convey the purpose for which it was designed.
A map is an incomplete representation or perception of the territory. The map offers the public only what the cartographer wants to show. The designer selects in a reasoned way the elements he wishes to map, but his choice depends on his own knowledge, sensitivity and intentions (Rekacewicz, 2006).
10.1. GIS Book: Symbology of points, lines and polygons.
Symbology allows you to define how each element will be displayed on the map (symbols, colors, frames, text). It must be decided whether or not it is required to display the information according to the attribute table of each layer. To configure the symbology of the layers created in section 6.1, right click on the layer to be customized (buildings), select Properties, and click on the Symbology tab.
On the Symbology tab, to represent geographic information, the following aspects must be considered for its configuration:
- Show: This is on the left-hand side of the window. It allows information to be organized individually, by categories, numbers, graphs and multiple attributes. For the building layer, select Categories > Unique values.
- Valued Field: Select the Type field to represent in categories the information stored within the same field. Clicking Add All Values adds all categories, clicking Add Values adds categories individually, Remove deletes the selected category and Remove All deletes all added categories.
- Color Ramp: A default color palette can be selected.
When you add all the categories of a layer, by default, <all other values> are added, it is recommended to uncheck the box. You can also remove the tag (Type) from the <Heading> header (see Figure 50). To see the changes in the table of contents click Apply and to accept them click OK. It is recommended to arrange the layers according to their geometry within the table of contents. The same procedure can be applied to the road_network and plant_cover layers to add all their categories based on the information contained in the attribute table.
In the table of contents, the List By Drawing Order button must be enabled to drag and drop layers in the required order (e. g. polygon at the bottom, lines in the middle and finally points on top).
By default each layer has exactly the same file name (Figure 51 left) and each category has the name according to the attribute table (Figure 51 center). To edit the name of a layer or category, click on it and you can change it individually. It is important to check that everything is written correctly (Figure 51 right), because the map legend will show those names.
When a layer is first loaded into ArcMap it is assigned symbols of the same size, shape and color (Single Symbol). In order to represent the real world through a map, it is necessary to use appropriate symbols that can properly represent the nature of the information.
ArcMap contains an extensive library of symbols used in various disciplines. The symbol that conveys what really needs to be represented must be carefully chosen. The symbol for each point in the list can be sorted individually. For example, to customize the School symbol (from the Buildings points layer) you must perform the following steps (Figure 52):
- Double click on the layer (or directly in the symbol).
- Double click on the symbol in the list.
- In the Symbol Selector window, click the Style Reference button.
- Check the Civic checkbox (or the required symbol libraries).
- In Symbol Selector select the School 1 symbol.
- In the Color button select the black color from the drop-down list (to customize click More Colors, in the Color Selector window you can customize RGB values).
- Select the size of the points layer symbol in the Size button. For lines, select Width for the line width, for polygons select Outline Width for the contour line width, and select Outline Color for the color of the contour line.
For the remaining layers, assign the symbology according to Table 5 based on the process described in the previous paragraph.
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