Analyzing Crime Data in Ottawa using QGIS

Introduction

The main purpose of this tutorial is to identify trends in crime in the Ottawa region using open source software. QGIS is the software that will be used for this tutorial. QGIS version 3.14 "Pi" can be downloaded here: (https://www.qgis.org/en/site/forusers/download.html). The data includes many different types of crimes that occurred in Ottawa from 2005 to 2013. The sub regions include: Orleans, Innes, Barrhaven, Kanata North, West-Carleton March, Stittsville-Kanata West, Bay, College, Knoxdale-Merivale, Gloucester-Southgate, Beacon Hill-Cyrville, Rideau-Vanier, Rideau-Rockcliffe, Somerset, Kitchissippi River, Capital, Alta Vista, Cumberland, Osgoode, Rideau-Goulbourn, Gloucester-South Nepean and Kanata South. Some examples of the crimes in the data set are: Total Criminal Code of Canada (CCC) including Traffic, Total Criminal Code of Canada (CCC) excluding Traffic, Crimes against Person, Total number of Homicides, Total Number of Attempted Murders, Total Number of Robberies and Total Number of Assaults (including Sexual Assaults), Total Number of Other Sexual Offences, Number of Abductions, Total Number of Uttering Threats or Intimidation Offences and Total Number of Other Crimes.

Where to get the data?

Based on the statistics that the Ottawa Police Service have provided, the MADGIC librarians at Carleton University created the shapefiles and they are available for download from the MacOdrum Library website. Considering it is an open source dataset, no login information is required.

The shapefiles are available for download at this link: http://madgic.library.carleton.ca/deposit/GIS/Crime_Statistics.zip

Loading the Dataset into QGIS

The first step to analyzing the data is adding it into QGIS. To do so, select the Add Vector Layer symbol. In QGIS 3.14, the Add Vector Layer button is accessible by clicking the Layer dropdown on the top toolbar. From there, navigate to Add Layer and Add Vector Layer. Adding vector layers can also be done by pressing Ctrl+Shift+V on a Windows computer or a Linux machine. Locate the folder where all of the (.shp) files were extracted. You can select to filter by ESRI Shapefile in the bottom right corner to make it easier as there are other types of files in the dataset that were downloaded.

The dropdown to filter for ESRI shapefiles only. This dropdown can help during instances where datasets contain dozens of other types of files.

Transforming the Coordinate System

When using GIS software, using the correct coordinate reference system is detrimental in terms of properly analyzing spatial data. Ensuring that all data frames have the same projection allows all of the data frames to align properly. To start the analysis, we will transform the coordinate system to WGS 1984 UTM zone 18N, which is the UTM zone for Ottawa.

This is how the shapefiles look after importing them into QGIS. The City of Ottawa appears to be warped. To change this, hover to Project>Properties (as a shortcut on Windows or Linux machines, Ctrl+Shift+P also brings you to Project Properties).

Under the CRS frame, you can search for any coordinate reference system under the Filter box. To find the coordinate system we are working with easier, search for "UTM zone 18N". On the map in the bottom right, QGIS will highlight where the UTM zone is assigned to. In this case, UTM zone 18N spans over the City of Ottawa.

After the layer coordinates have been transformed, the map appears to be less warped. Ensure that all of the layers have the same coordinate system. Repeat this step for all of the crime data layers that were imported.

UTM map of the world. Photo source: https://www.maptools.com/tutorials/grid_zone_details

Introduction to Layer Properties

Layer Properties can be opened by right clicking any of the layers and clicking Properties. This opens the Layer Properties window. From here, several aspects of the layer can be edited. Some examples include layer title, symbology, labels and so on.

General Settings

Under Source:

• Layer name can be modified and changed to anything. Changing layer names is key to be able to identify different layers. In the case that the data layers came without clear labels, labelling them by year is crucial in order to easily identify each data set.
• Data source encoding can be changed (System, Windows, and Macintosh for example)
• Coordinate Reference System can be changed
• Scale dependency can be turned on to restrict the minimum and the maximum scale

Labels

Labels can be used in any vector layer. Some label settings include:

• Text (Able to modify the size, font style, transparency, color and style of text)
• Formatting (Able to modify the line height and alignment)
• Buffer
• Background (Able to modify the background settings)
• Shadow (Use this setting to add depth to labels by adding shadows)
• Placement (Use this setting to modify the placement of the labels, including distance from centroid)
• Rendering (Able to perform scale based visibility and pixel based visibility)

Fields

Within the Field Properties tab, you can edit the field data as well as create new fields using the Field Calculator. Any new fields you create will appear at the bottom of the field list.

To create a new column in the attribute table, open Fields under Properties and click the Area Calculator button. Here we will start to calculate the population density of crimes for years 2016, 2013 and 2010. The data downloaded does not contain the area km^2 value that is needed to calculate population density of crimes. Therefore, it needs to be created. Under Field Calculator, the first step is to calculate area km^2. In the Expression box, enter the calculation $area/1000000. Enter an output field name (In the example, "area km ^" was used), and click OK. When doing calculations in the Field Calculator, if an expression is invalid, it will state "Expression is invalid" in red.

Creating the population density field

The total population divided by the area will result in the population density. We will calculate population density for layers 2010, 2013 and 2016.

To calculate population density, insert the function (pop2016/"area km2") into the calculator. Area km2 is the attribute that was created in the previous step. The area km^2 attribute that was just created can also be found under the Fields and Values tab.

Rendering

Rendering can be used to simplify the geometry. Under the Rendering tab, simplification threshold and scale can be customized to enhance the rendering process.

Additional Settings under Layer Properties

Additionally, under Layer Properties, other tools such as Legend, Actions, Joins, Display and Variables can be accessed.

Using Style and Diagram Functions under Layer Properties

Style Function

Under Style there is a dropdown menu, which the Single Symbol, Categorized, Graduate, Rule Based, Point Displacement, Inverted Polygons and Heat Map can be selected. For the purpose of this tutorial I am mainly going to focus on the Graduate Style.

Single Symbol

Single Symbol Function is useful for showring the features without any sort of categorization. An example below demonstrates a map of Ottawa without any sort of categorization.

Categorized Style

Categorized style is useful for demonstrating areas in the City of Ottawa. To symbolize the map this way, right click any layer (in this case, the crime wards in 2010 is used), and go to Symbology.

Select ward_Name as the value, and select Classify on the bottom left corner.

Under the Labels tab in Layer Properties, click Single Labels and select ward_Name for the value. This will generate labels for each ward in the City of Ottawa.

Graduated Symbols

Graduated Symbols are useful for displaying the features based on their numerical values. First, the style of symbology needs to be selected as Graduated under the Symbology tab. The value that will be classified is the Population Density attribute that was created earlier. Select "pop_den" from the Value dropdown.

Map demonstrating population density in the City of Ottawa in 2010, using graduated symbols and labels.

Map demonstrating total number of robberies by ward in the City of Ottawa in 2010, using graduated symbols and labels.

Using the Graduated Symbols function, it is apparent from the map that there is a higher population density in the downtown core of Ottawa. From observing the second map, there were more robberies in the downtown core in 2010 as well.

Diagrams

Diagrams are useful for showing multiple features on a single layer. To access diagrams, open Layer Properties and navigate to Diagrams. On the dropdown in Diagrams, select Pie Chart. Below, all of the attributes in the selected layer (in this case crime wards in 2010) will be displayed. For the purpose of this tutorial, total number of robberies, abductions and assaults are used as attributes in the pie chart.

At first, the pie charts can be too large and cover most of the map, similar to this:

To counter this, open Diagrams again and navigate to Size. There, the pie chart (or other diagrams) size can be adjusted. For the sake of the tutorial, size 7 will be used.

This is how the map looks when the size of the pie charts were reduced.

Cartographic Design and Crime Data in Ottawa

While QGIS is a powerful tool that allows users to visually analyze data and compare them on maps, sometimes a final product is required. There are many cartographic aspects that are behind maps such as colour, scale, legend, north arrow, labelling and title. Using these cartographic aspects, we can make a map displaying any variable in the attribute table. For this tutorial, the crime wards data from 2016 will be used. The variable that is used is asslt_num, total number of assaults in Ottawa in 2016. However, any variable in the attribute table can be used. Similar to earlier in the tutorial, open Layer Properties and navigate to Symbology. There, select Graduated.

Graduated menu where users can adjust color ramp, class and variable.

Next, to create a final product, navigate to Project>New Print Layout (or click Ctrl+P on Windows and Linux machines). It will bring up a separate menu. To add the map created in the main menu of QGIS, navigate to Add item>Add Map. Highlight the work area and the map will appear.

It's possible that the map will appear small on the project layout. To adjust the size of the map, the scale needs to be adjusted. The scale used for this project is 500000.

The scale is located on the right side bar under Main Properties.

Next, a legend is required. Navigate to Add Item> Add Legend. Similar to importing the map, drag the cursor along the project working area.

Because there are so many layers present in QGIS, the legend appears with a lot of attributes, many that are not relevant to the project being worked on. To remove these from the legend, navigate to the right toolbar and uncheck "Auto update". From there, anything not wanted on the legend is able to be deleted using the delete button.

Delete anything that doesn't belong to the crime wards in 2016 layer.

The legend will now look like this.

Additional Statistics

Additional statistics can be obtained under Vector tab/Analysis tool/Basic Statistics. Input Vector Layer needs to be selected then type of crime needs to be selected. As a result it will show the mean, standard deviation, sum, min, and max, number of unique values, range and median.

Different Scenarios

Scenario 1 (Comparing the Impaired driving data from 2005, 2010 and 2013)

Quick Analysis: The number of impaired driving occurrences in suburbs (Kanata, Cumberland) from 2005 to 2010 has become lower. However the number of impaired driving occurrences in east end from 2010 to 2013 has become significantly higher, and the number of impaired driving occurrences increased dramatically in College ward in from 2005 and 2010 to 2013.

Scenario 2 (Analyzing the total number of violent crimes, the total number of assaults and the number of traffic offences from 2010 data using Diagrams )

The diagrams are showing that the western and the southern areas of Ottawa have less number of violent crimes, assaults and traffic offences even though they have relatively similar population density. Somerset ward has the highest population density as well as the highest number of violent crimes, assaults and traffic offences.

Conclusion

Conclusively this tutorial highlights that QGIS was a powerful open source GIS software for analyzing the crime trends in Ottawa from 2005 to 2013. There are many other different crimes to analyze from, only limited number of crimes were highlighted in this tutorial. The QGIS software can be downloaded from the website highlighted above and the crime data can be downloaded from the MacOdrum Library website mentioned above for further analysis.

Reference List

• Ottawa Police Service Crime Data. (2013).

The data is gathered from the Carleton University MADGIC Desk’s website.

Ottawa Police Service Crime Data retrieved from: http://madgic.library.carleton.ca/deposit/GIS/Crime_Statistics.zip

• QGIS 3.14 ("Pi") Software, which was downloaded from:

https://www.qgis.org/en/site/forusers/download.html