Creating Service Areas from an Interactively Chosen Point
Included in this tutorial:
Accessing and Opening the Service Area (from point) Tool
Service Area (from point) Parameters, including the standard inputs, advanced options, and output options
Examining the results of an example
Software version in examples: QGIS 3.22
Tutorial Data: The tutorial includes demonstration with sample data available here.
Credits: L. Meisterlin with Varisa Tanti and Nikolas Michael (2022)
This tutorial covers creating service area polygons from an location chosen interactively within a map view, using the Service Area (from Point) tool in QGIS.
Note: The tutorial demonstrates using the Network Tutorials Data Package available with other sample data here.
Opening the Service Area (from point) Tool
The path to opening the Service area (from point) tool is Processing > Network analysis > Service area (from point).
You can access the Service area (from point) tool by clicking Processing in the main menu, and clicking through Network Analysis > Service area (from point).
Service area (from point) Parameters
In the Service area (from point) dialogue box, you will see several parameter options.
The demonstration below hovers over and expands these different parameters. (Left clicks are shown in magenta.) In the demonstration example, we choose to calculate a 1,000-foot service area from a central point (chosen interactively).
The input options are listed and described below.
demonstrating the input options of the Service Area (from Point) tool
the Standard Inputs
Vector layer representing network: Select vector (polyline) layer representing the network. This layer should be topologically appropriate for network-based analysis (i.e., its connectivity relationships should be accurate). In the example, the only polyline layer within the project is pre-populated as the default option.
Path type to calculate: Select if you want to find the shortest or fastest route. The “shortest” option will measure distance based on the geometry of the input features. The “fastest” option will measure based on time (you will specify how time is calculated further in the dialogue box). In the example, we choose to calculate the shortest route.
Start point: This is the starting point of your network. After clicking the “ellipses” button, click the map canvas to choose the start location. In the example, we zoom in to choose a central location.
Travel cost: Type a value for the distance or time to travel from the start point. Distance is measured in the units of the network layer’s CRS. Time units are measured hours. In the example, we choose to calculate a service area that is 1,000 feet from the start point.
Advanced (Specific) options
The Advanced options specify how direction, time, and other network parameters are determined and treated in the analysis. (It helps to remember that these aren’t really “advanced” options as much as they are “specific” options.)
In our example, we are not specifying constraints on direction and we are not using speed to measure a time-based travel cost.
Direction options: If modeling direction is relevant for your service areas (for driving, for example), you specify the direction parameters with the first several fields here.
The Direction Field is the field in the network layer’s attribute table containing direction information.
The Value for forward, backward, or both directions options allow you to specify which values within the Direction Field correspond to particular directions along the network’s edges.
The Default direction option allows you to specify the directional movement along a network’s edge if no value or field is specified.
Speed (time) options: The Speed Field is the field in the network layer’s attribute table containing the speed at which movement occurs across each edge of the network.
The Default Speed option allows you to specify a constant speed if no Speed Field is specified (in kilometers per hour).
The Topology tolerance option allows you to specify a tolerance (specify units as well using the drop-down) for connectivity within your network layer. In our example, because the input vector layer has been prepped for topological accuracy, we do not need a topological tolerance.
Service Area Output options
The output options for this tool include lines along the network from the start point and/or points generated at nodes along the network. Generating polygons is not an option. To generate a polygon feature representing the service area, create a convex hull from either of these outputs.
Service area (lines). Indicate if the output will be created as a temporary layer, saved to a file, saved to a geodatabase, saved to a database table, or will not have an output.
Service area (boundary nodes) Indicate if the output will be created as a temporary layer, saved to a file, saved to a geodatabase, saved to a database table, or will not have an output
Open output file after running algorithm: Check either of these boxes to add either of the service area output options to your project.
In our example, we select both options—saving them as temporary files and adding them to the project.
Examining the Example’s Results
As expected, the results of our example are two temporary layers: Service area (lines) and Service area (boundary nodes). The former includes the edges (or portions of edges) within 1,000 feet from the central start point we clicked, measured along the input vector lines. The latter includes the network nodes within that distance and the node points at the farthest (1,000 feet) distance measured.
the two outputs created from the example options
From the attribute tables, we can see that both layers include only a single feature, comprising all the nodes or edges of the output respectively. These single-feature layers can be converted to multiple features using other geoprocessing tools (e.g., the “Explode lines” tool).
the two output attribute tables