Editing Vector Data in GRASS GIS - Revision history

Ali Awde at 18:30, 6 October 2026

2026-10-06T18:30:24Z

Ali Awde at 18:26, 6 October 2026

2026-10-06T18:26:12Z

Ali Awde at 18:25, 6 October 2026

2026-10-06T18:25:11Z

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Ali Awde at 13:20, 22 September 2026

2026-09-22T13:20:23Z

Ali Awde at 13:20, 22 September 2026

2026-09-22T13:20:02Z

SheaTimmins at 18:23, 22 December 2022

2022-12-22T18:23:34Z

SheaTimmins at 19:10, 21 December 2022

2022-12-21T19:10:08Z

SheaTimmins at 19:08, 21 December 2022

2022-12-21T19:08:28Z

SheaTimmins at 18:59, 21 December 2022

2022-12-21T18:59:53Z

SheaTimmins at 18:57, 21 December 2022

2022-12-21T18:57:17Z

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 This tutorial will introduce basic GRASS GIS tools for working with vector data and editing aswell. This will include the use of three open datasets from the open source site of the City of Ottawa: Traffic Collisions, Red Light Camera Violations and Road Centrelines. The tutorial on this page will cover the creation of a GRASS project, importing the vector data, selecting specific features using attribute conditions, changing vector symbology and the use of basic vector editing tools.
-If you currently DO NOT have GRASS GIS installed, this is the link to download it, including installation instructions. [https://dges.carleton.ca/CUOSGwiki/index.php/Intro_to_GRASS_workshop]
+If you currently DO NOT have GRASS GIS installed, this is the link to download it, including installation instructions. [https://dges.carleton.ca/CUOSGwiki/index.php/Intro_to_GRASS_workshop Intro to GRASS workshop]
 == Data ==

@@ Line 37: / Line 37: @@
 This step is important because some downloaded shapefiles may have filenames that do not meet GRASS vector map naming requirements.
-[[File:GRASS Red Light Output Name.png|500px|thumb|left|Setting a valid output vector map name before importing the Red Light Camera Violations dataset.]]
+[[File:GRASS Red Light Output Name.png|500px|thumb|center|Setting a valid output vector map name before importing the Red Light Camera Violations dataset.]]
 Run it. Repeat this import process for '''Traffic_Collision_by_Location_2019''' if it is not already present in the Project.
@@ Line 47: / Line 47: @@
 * '''Traffic_Collision_by_Location_2019'''
-[[File:GRASS Three Vector Layers.png|500px|thumb|left|The three Ottawa vector datasets loaded into the GRASS GIS Project.]]
+[[File:GRASS Three Vector Layers.png|500px|thumb|center|The three Ottawa vector datasets loaded into the GRASS GIS Project.]]
 == Filtering and Displaying the Vector Data ==
@@ Line 61: / Line 61: @@
 Open the SQL builder, beside the SQL WHERE condition. Click '''TOTAL_VIOL''', then select the '''>=''' operator, and enter '''500'''.
-[[File:GRASS Red Light Selection Tab.png|500px|thumb|left|The Selection tab provides access to the SQL Builder for filtering vector features.]]
+[[File:GRASS Red Light Selection Tab.png|500px|thumb|center|The Selection tab provides access to the SQL Builder for filtering vector features.]]
 It should look like this " "TOTAL_VIOL" >= 500 "
-[[File:GRASS Red Light 500 Filter.png|500px|thumb|left|SQL query used to display Red Light Camera locations with 500 or more violations.]]
+[[File:GRASS Red Light 500 Filter.png|500px|thumb|center|SQL query used to display Red Light Camera locations with 500 or more violations.]]
 Apply the changes in SQL then apply it in the layer properties. The Red Light Camera will now only display locations with 500 or more violations in 2019.
@@ Line 73: / Line 73: @@
 This exact process will be repeated for the '''Traffic_Collision_by_Location_2019''' layer. In the SQL Builder, you will select '''Total_Coll''' and >= 10 .
-[[File:GRASS Traffic Collision 10 Filter.png|500px|thumb|left|SQL query used to display locations with 10 or more traffic collisions.]]
+[[File:GRASS Traffic Collision 10 Filter.png|500px|thumb|center|SQL query used to display locations with 10 or more traffic collisions.]]
 Apply it and the layer will now display only locations with 10 or more collisions.
@@ Line 81: / Line 81: @@
 The two point layers can be very hard to distinguish when they are the same similar symbols. we will now change the colors, shapes and sizes to make them easier to interpret.
-[[File:GRASS Traffic Collision Symbol.png|500px|thumb|left|Changing the Traffic Collision point symbol to a circle with a size of 6.]]
+[[File:GRASS Traffic Collision Symbol.png|500px|thumb|center|Changing the Traffic Collision point symbol to a circle with a size of 6.]]
 ==== Traffic Collision Symbology ====
@@ Line 91: / Line 91: @@
 Go to the '''Colors''' tab and change the '''Area fill color''' to yellow. Click '''Apply''' to update the map display.
-[[File:GRASS Traffic Collision Colors.png|500px|thumb|left|Changing the Traffic Collision feature color to green and the area fill color to yellow.]]
+[[File:GRASS Traffic Collision Colors.png|500px|thumb|center|Changing the Traffic Collision feature color to green and the area fill color to yellow.]]
 ==== Red Light Camera Symbology ====
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 You can use the Zoom In tool to focus on somewhere in Ottawa, where many of the displayed locations are concentrated.
-[[File:GRASS Red Light Camera Color.png|700px|thumb|left|Changing the Red Light Camera Violations feature color to red.]]
+[[File:GRASS Red Light Camera Color.png|700px|thumb|center|Changing the Red Light Camera Violations feature color to red.]]
 == Editing Vector Features ==
@@ Line 112: / Line 112: @@
-[[File:GRASS Vector Digitizer Roads.png|700px|thumb|left|The Road Centrelines layer opened in the GRASS GIS Vector Digitizer.]]
+[[File:GRASS Vector Digitizer Roads.png|700px|thumb|center|The Road Centrelines layer opened in the GRASS GIS Vector Digitizer.]]
 === Moving a Vertex ===
@@ Line 118: / Line 118: @@
 Select the '''Move vertex''' tool from the Vector Digitizer toolbar. Click a vertex on a road feature, move it to a new position, and click again to place it.
-[[File:GRASS Move Vertex Tool.png|700px|thumb|left|Road Centrelines displayed in the Vector Digitizer while using the Move vertex tool.]]
+[[File:GRASS Move Vertex Tool.png|700px|thumb|center|Road Centrelines displayed in the Vector Digitizer while using the Move vertex tool.]]
 If you are only trying the tools out, use '''Undo''' after moving the vertex to return the road feature to its original geometry.
@@ Line 128: / Line 128: @@
 An attribute window will open and display the fields associated with the selected feature.
-[[File:GRASS Update Vector Attributes.png|600px|thumb|left|Viewing the attributes of a selected road feature using the Vector Digitizer.]]
+[[File:GRASS Update Vector Attributes.png|600px|thumb|center|Viewing the attributes of a selected road feature using the Vector Digitizer.]]
 Attribute values should only be changed when there's a valid reason to modify the data. For this tutorial, viewing the attributes is sufficient to demonstrate the tool.

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-== '''Introduction''' ==
+== Introduction ==
 This tutorial will demonstrate how to do a vector analysis using GRASS GIS. By the end, you should be a little more comfortable using the program. Please note that for this tutorial we are using GRASS 8.2, older versions of GRASS may not reconcile with this tutorial. Our goal is to use the 2020 Red Light Camera Violations data from open.ottawa.ca to make a map that displays the safest areas in Ottawa to drive based on the number of traffic violations. If you do not already have GRASS installed on your computer, you can go to this [https://dges.carleton.ca/CUOSGwiki/index.php/Intro_to_GRASS_workshop Intro to GRASS workshop page] with detailed instructions on how to download it.
-== '''Data''' ==
+== Data ==
 First we will need to download our data. You can download the Ottawa Traffic Collision data [https://open.ottawa.ca/datasets/ottawa::traffic-collision-by-location-2019/explore?location=45.250250%2C-75.806856%2C1.62 here.] After you proceed to the link, click the download button, and select "shapefile." Once you have downloaded the Traffic Collision data, click [https://open.ottawa.ca/datasets/ottawa::red-light-camera-violations-2019/explore?location=45.376580%2C-75.686783%2C2.96 here] to download the Red Light violations data. Finally, download the Road Centrelines data [https://open.ottawa.ca/datasets/ottawa::road-centrelines/explore?location=45.245509%2C-75.794650%2C1.87 here.]
-== '''Getting Started with Grass''' ==
+== Getting Started with Grass ==
 Start by launching the GRASS software. You should see three windows, one is a terminal, one is the Map Display, and one is the main interface that includes tabs along the bottom of the window such as "data" and "layer," which we will refer to as the Layer Manager for convenience. You need to add a new "database," which is essentially a folder that you will keep "locations" in. Within the "locations," you will store your mapsets.

@@ Line 1: / Line 1: @@
-== Introduction ==
+== '''Introduction''' ==
 This tutorial will demonstrate how to do a vector analysis using GRASS GIS. By the end, you should be a little more comfortable using the program. Please note that for this tutorial we are using GRASS 8.2, older versions of GRASS may not reconcile with this tutorial. Our goal is to use the 2020 Red Light Camera Violations data from open.ottawa.ca to make a map that displays the safest areas in Ottawa to drive based on the number of traffic violations. If you do not already have GRASS installed on your computer, you can go to this [https://dges.carleton.ca/CUOSGwiki/index.php/Intro_to_GRASS_workshop Intro to GRASS workshop page] with detailed instructions on how to download it.
-== Data ==
+== '''Data''' ==
 First we will need to download our data. You can download the Ottawa Traffic Collision data [https://open.ottawa.ca/datasets/ottawa::traffic-collision-by-location-2019/explore?location=45.250250%2C-75.806856%2C1.62 here.] After you proceed to the link, click the download button, and select "shapefile." Once you have downloaded the Traffic Collision data, click [https://open.ottawa.ca/datasets/ottawa::red-light-camera-violations-2019/explore?location=45.376580%2C-75.686783%2C2.96 here] to download the Red Light violations data. Finally, download the Road Centrelines data [https://open.ottawa.ca/datasets/ottawa::road-centrelines/explore?location=45.245509%2C-75.794650%2C1.87 here.]
-== Getting Started with Grass ==
+== '''Getting Started with Grass''' ==
 Start by launching the GRASS software. You should see three windows, one is a terminal, one is the Map Display, and one is the main interface that includes tabs along the bottom of the window such as "data" and "layer," which we will refer to as the Layer Manager for convenience. You need to add a new "database," which is essentially a folder that you will keep "locations" in. Within the "locations," you will store your mapsets.

@@ Line 79: / Line 79: @@
 ===Displaying Layers Based on Attribute Data===
-The first thing we will edit in our Map display is the Red_Light_Camera_Violations_2019.shp data. We are going to display only the intersections that have 700 or more traffic violations in the year of 2019.
+The first thing we will edit in our Map display is the Red_Light_Camera_Violations_2019.shp data. We are going to display only the intersections that have 500 or more traffic violations in the year of 2019.
 Right-click on Red_Light_Camera_Violations_2019.shp and select "Properties."

@@ Line 146: / Line 146: @@
 <br />
 <br />
-Next we are going to edit the symbol size and shape. Right-click on the Traffic_Collision_by_Location_2019 layer. Select “Properties,” then select the “Symbols” tab. Click on the “X” to change the shape of the symbol. Select the circle as the new symbol. Next change the symbol size to 6. Your “Symbols tab should look like the photo below.
+Next we are going to edit the symbol size and shape. Right-click on the Traffic_Collision_by_Location_2019 layer. Select “Properties,” then select the “Symbols” tab. Click on the “X” to change the shape of the symbol. Select the circle as the new symbol. Next change the symbol size to 6. Your “Symbols" tab should look like the photo below.
 <br />
 <br />

@@ Line 164: / Line 164: @@
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 <br />
+==Conclusion==
+In this tutorial, you have begun to explore ways of editing your map display in GRASS GIS. By the end of it, you should be more comfortable uploading data into GRASS, and editing symbols in vector layers. There is much more you can do in this program, and hopefully this tutorial gives you the confidence and the basics to continue to explore the features of GRASS.

@@ Line 152: / Line 152: @@
 <br />
 <br />
 Before you press “Apply” and close this window, navigate back to the “Colors” tab and change the “Area fill color” to yellow. Then press apply. The Map Display should now look like the one below.
+<br />
+<br />
 [[File:symbolstuff.png|500px]]
+<br />
+<br />
+Now we will do the same thing for the Red_Light_Camera_Violations_2019 layer. Right-click on this layer, and select “Properties.” Then, go to the “Symbols” tab and change the symbol from “X” to a circle, and the size from 5 to 6. Before you press “Apply,” navigate to the “Colors” tab and select the color red for the “Area fill color.” You Map Display should now look like the one below.
+<br />
+<br />
+[[File:peachtea.png|500px]]
 <br />
 <br />