Creating Service Areas from an Input Feature Layer
Included in this tutorial:
Accessing the Service Area (from layer) tool
Reviewing the tools parameters and options
Running the tool (with an example) and examining its results
Software version in examples: QGIS 3.22 (Windows OS)
Tutorial Data: The tutorial includes demonstration with the Network Tutorial Data available here.
Credits: L. Meisterlin (2022)
This tutorial covers creating service area polygons from a point feature layer, using the Service Area (from Layer) tool in QGIS.
Opening the Service Area (from layer) Tool
You can access the Service area (from point) tool by clicking Processing in the main menu, and clicking through Network Analysis > Service area (from Layer).
Service area (from layer) Parameters
In the Service area (from Layer) 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 layer of four point features, called ExamplePoints (these were extracted from the point layer in the tutorial data package).
The input options are also listed and described below.
demonstrating the inputs and running the Service Area (from layer) processing 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, we choose our streets_ped layer, which is the only polyline layer within the project.
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.
Vector Layer with start points: Specify the point feature layer from which service areas will be calculated. In the example, we choose the ExamplePoints layer.
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 points.
Network (”Advanced”) 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 the options for building the network from the vector layer representing it.)
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 points 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 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 locations in the ExamplePoints layer, 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 results of the example Service Areas (from layer) tool process
From the attribute tables, we can see that both layers one feature per service area output, comprising all the nodes or edges of the output respectively. Thus, because our input “start points” layer included four locations, both outputs include four features. Note that their attributes include all of the attributes from the start points feature layer.
the resulting example attribute tables
If needed, these combined output features can be converted to single-point or single-segment feature classes using other geoprocessing tools (e.g., the “Explode lines” tool).