# Symbolize by Value
In this tutorial, we will learn how to change the style of data features based on their stored attribute characteristics. We will be working with MBTA subway rail lines to change the color of each line, depending on how each line feature is categorized.
# Get the data
We will be working with the MBTA Rapid Transit Data, made available by MassGIS.
You can download the data here.
How to Download
Select Download this data
This data is made available as multiple shapefiles zipped up into a compressed folder. You will have to unzip or uncompress the folder in order to access the data.
To learn more about different GIS file formats, please find our Common GIS File Formats guide.
# Bring the data into QGIS
If you do not already have QGIS, you will need to download the free software first. To learn how to download and use QGIS, please find the Get Started with QGIS guide.
Once you have a new QGIS project open, you can add the data to the project by selecting Layer > Add Layer > Add Vector Layer
Under Source > Vector Dataset(s) click the elipses Browse button to pull up the data browser.
Navigate to where you have downloaded and unzipped the data, and select the file named MBTA_ARC.shp
Select Open
Select Add
Drag and drop
You can also add the shapefile by simple dragging the file MBTA_ARC.shp from your file finder into the Map Canvas. Try it out!
# Inspect the data
When you first bring the data into QGIS, all of the lines appear to be the same color. There are values stored within the data about each line feature, giving us information about which subway line each feature is associated with. We can use these feature attribute values to apply symbology uniformly to the features on the map.
In the Layers window, right-click on the MBTA_ARC layer
In the options that appear upon right-click, select Open Attribute Table
Here, we are presented with a table of values in which each record corresponds to a line segment on the map. Each record has a value for its associated MBTA line. This LINE field, is the field we will use to symbolize the map.
You can close out of the Attribute table by clicking the red x in the top left corner of the window.
# Change the symbology method
In the Layers window, right-click on the MBTA_ARC layer
Select Properties
Select Symbology
At the very top of the symbology window, there is a drop-down menu where the default value is Single Symbol
WARNING
This drop down can be easy to miss!
Instead of symbolyzing every feature with one single color, we wish to symbolize them based on the subway line category they are grouped into.
Click the drop down that says Single Symbol and change to the menu option Categorized
Now we have told QGIS that we want to symbolize based on categories. Next, we have to tell QGIS which category to symbolize on.
In the next drop down, titled Column, click the down arrow on the menu, and select the field LINE
The top of your symbology window should now look like this:
Towards the bottom of the symbology window, there is a button labeled classify. Click the Classify button.
Now we will be able to edit each separate category of data within the field LINE
# Update symbology
Next, we will go through each subway line, and update its symbol.
Double-click the small line to the left of the word BLUE
A new window will pop up, allowing us to edit the symbology of all features categorized as being associated with the MBTA Blue line.
Click on the menu drop-down labeled Color
Under HMTL Notation replace the current value with the following hex color value
Blue:
#007AB0
Press OK
Let's also make the lines thicker.
In the menu labeled Width, replace the current value by typing in 1.5.
Press OK
Repeat the same process for all of the different subway lines.
Red:
#DA484C
Green:
#008B60
Orange:
#E7A15F
Silver:
#8B8C86
When you are done with all the categories, select OK
The lines should now be appearing on the map with the proper colors.
You can now use this data alongside other data, or add a basemap for reference.
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