Today we are going to learn about how to change the symbology of a layer, reviewing different types of legends that are available in gvSIG Desktop.

The symbology is one of the most important properties of a layer. gvSIG includes a great variety of options to represent layers with symbols, graphs and colours. Excepting unique symbol option, the rest of legends are assigned to each element depending on their attribute values and the properties of the type of legend selected.

By default, when a layer is added to a View, it’s represented with a unique symbol with random colour, that means, all the elements of the layer are represented with the same symbol. To modify the symbology of a layer we have to access to its “Properties” window and select “Symbology” tab. We are going to open our “Game of Thrones” project and we will start to explore this part of gvSIG Desktop.

If we want to change a symbol, the easiest way is double-clicking on it at the ToC (Table of Contents with the list of layers). A new window will be opened to select the new symbol. For example we are going to double-click on the symbol of the “Rivers” layer.

At the new window we can change the colour and the width of the line, press on any of the symbol libraries installed (“gvSIG Basic” by default, although we can install a lot of libraries from the Add-ons Manager). In this case we are going to change width to 3 and select a dark blue colour. We press “Accept” to apply changes.

Now we are going to see the type of legends that are available and we will select a legend by the different types of locations, attribute that we have used in the previous posts. There are a lot of possibilities for symbology, and you can see this additional documentation.

Firstly we will have to open the “Properties” window of the layer. Activating the layer we will find this option at the “Layer/Properties” menu, or directly using the secondary button of the mouse on it. 

Now we access to the “Symbology” tab and a window is shown with the symbology applied. At the left side we can find all the types of symbols than we can use. Warning: Depending on the type of layer (point, line or polygon) we can find different legends available.

In this case we are going to select a legend about “Categories/Unique values”. This type of legend is used to assign a symbol to each unique value specified at the attribute table of the layer. Each element is drawn depending on the value of an attribute that identifies the category. In our case we will select “Type” for classification field; we press “Add all” and it will show the legend created by default:

The Labels (at the right side) can be modified. You can change the texts here.

Now, double-clicking on every symbol a new window will be opened where we can modify them or select new symbols from our symbol libraries with “Select symbol” option. Once they are selected we press “Apply” and we will see the results in our View. 

The best way to learn different type of legends is testing… We also recommend you to install and check the different symbol libraries that are available in gvSIG (hundreds of symbols of all types!!)

See you in the next post…