Travel Distance Overlay Tutorial
Prerequisites
The following prerequisites should be met before starting this tutorial:
- This tutorial relies on base knowledge about the editor interface. It is also recommended to have completed the tutorial(s) related to the Combo Overlay. If you have not yet followed the tutorials related to those subjects please do so first.
- This tutorial can be followed with any Project based on real data with houses and a network of roads
Introduction to the Travel Distance Overlay
The Travel Distance Overlay is a spatial calculation for determining whether it is possible to reach a given destination (or one of multiple destinations), from any given location, via a pre-defined network of allowed routes. In contrast to simpler Distance Overlay calculations, which performs calculations "as-the-crow-flies", the Travel Distance Overlay specifically takes into account whether it is actually possible where movement is possible. This creates a more practical result in terms or reachability.
The calculation works by establishing a collection of relevant "destinations", and determining a valid grid of "traversable" locations. Then, starting at the destination and only taking into consideration traversable grid cells, each adjacent cell is marked as reachable. Cells adjacent to those are also marked as reachable, and this process is iteratively repeated until the distance covored by such as a sequence of adjacencies has reached the maximum amount of distance to compute. In other words, starting at each "destination", valid routes propagate across the network of allowed traversable routes until the maximum distance has been reached.
The Travel Distance Overlay can be used to calculate which locations can be reached when starting at a specific point of interest. It can equally be used to calculate from which location it is possible to reach a point of interest. Mathematically, these calculations are identical, just reversed in conceptual direction.
For completeness' sake it is prudent to state: the Travel Distance Overlay uses the term "Destination" for the locations to calculate from- and to-, and in terms of implementation the calculation starts out at these destinations.
Creating a simple Travel Distance calculation
A Travel Distance Overlay requires two spatial inputs: destinations and traversables.
Projects created with real world data virtually always include some form of road network, which a Travel Distance Overlay will use by default as its traversable input. Destinations must always be explicitly provided, either by manually drawing in relevant locations, importing them from an external source or file, or by calculating them on-the-fly.
Next, the most important setting for a Travel Distance Overlay is the maximum allowed travel distance, which is a simple numerical setting.
Setting up a destination
Begin by setting up a dataset of one or more destinations of interest. Find a place in the Project map which it would be relevant to travel to, such as a park or other outdoor recreational location.
Add a new Area to the Project.
A new Area is now added, and selected in the left panel.
Its details are displayed in the right panel.
At the bottom of the right panel, click on "Adjust Area" to start manually drawing it in the Project map.
Draw it in the location of a park or similar recreation area. Ensure that it overlaps with the road network.
When drawn in properly, click on "Apply Selection".
In the right panel, switch to the Attributes tab.
At the bottom of the right panel's list of Attributes, fill in the form for a new Attribute with the following input:
- Name: RECREATIONAL_DESTINATION
- Values: 1
Click on "Save New Attribute" to add the Attribute to the Area.
With these steps an Area has been added to the Project map indicating a Destination Area we can use with the Travel Distance Overlay.
Configuring a Travel Distance Overlay
Add a Travel Distance Overlay.
A Travel Distance Overlay is now added, and selected in the left panel.
With the Overlay selected in the left panel, its details are displayed in the right panel.
Click on "Configuration Wizard".
This opens the Configuration Wizard which will assist in setting up the Travel Distance calculation.
Continue to Step 1.2 (skipping over any intermediate steps).
This step allows for configuring the destinations of the Travel Distance Overlay.
Click on "Select existing Destination Areas based on Attribute".
This will show a dropdown with which to select the Attribute marking the Areas to be used as destinations for the calculation.
Change the dropdown to "RECREATIONAL_DESTINATION", the Attribute previously added to the Area created earlier.
Continue to step 2.
This step allows for setting the numerical parameters for the Travel Distance Overlay's calculation. There are 2 parameters available, the most important of which is the Max travel distance.
Set the "Max travel distance" to 400 (m).
These are all the configurations needed.
For the sake of insight, continue to step 3.1 (skipping over any intermediate steps).
This step allows for the configuration of which mode of travel should be taken into account for the Travel Distance Overlay's calculation. By default, travel by cars is the selected mode of travel. This is the default because it is the most clear based on default data sources.
Although it is possible to configure the Travel Distance Overlay to take into account (or use exclusively) any other mode of travel as well, additional configrations elsewhere in a Project will be required to set those up properly. Therefor, it is often more efficient (and a good enough indication) to use cars as mode of travel for a general indication of reachability.
(This relies on the assumption that in urban environments where cars can travel, most car routes are accompanied by routes for pedestrians and bicycles.)
Finish and close the Configuation Wizard.
With the Travel Distance Overlay now configured, click on "Update Now" to let the Project recalculate.
Inspecting the results
The Overlay will show results in the form of a blob, spread out starting from the Destination Area and propagating over the roads, with a buffered distance from the route it has traveled.
All locations in this blob can be reached from the previously defined Destination Area, and when starting from any of those locations it is possible to reach the Destination Area.
The buffering is so that the end-result of the calculation is not merely which parts of the road network are reachable (or within reach), but that the results actually "hit" the Buildings nearby. This means the results can be used directly to match with specific Buildings and whether those Buildings are in range of a Destination Area.
For one Destination Area result, it will be a single color spread out. When multiple discrete Destination Areas exist, each Area will result in a unique value and coloring, showing which Destination Area is effectively "closest" or "most immediately reachable".
Assignments
- Add one or more additional Destination Areas to the Project. Place them in locations distinct from each other and from the Destination Area already present. Recalculate and observe the result.
- Using the Configuration Wizard of the Travel Distance Overlay, modify the Distance to road setting to a lower value. Recalculate the Overlay, and take note of the effect on the spatial calculation.
Advanced destinations for the Travel Distance calculation
While the basic Travel Distance Overlay setup can perform simple travel distance calculations with static and automatically provided data, it is possible to create more complex and dynamic calculations by using prequels. The ability to use (pre-)calculated prequels allows for two important additions: the ability to clean up or improve the inputs to handle minor imperfections, and the ability to the fully determine the traversable network or the destinations.
Previously, a Destination Area was drawn manually, specifically overlapping with with the intended point of interest and the network.
However, commonly datasets don't have the same excessive overlap. This can be for a number of reasons. Foremost, points of interest are usually structured as point features. And when such features are defined as polygons, it is usually an exact fit, and any intermediate feature between the actual Building or location, and the actual road network, is excluded. Both of these situations cause there to be a distinct distance between the Destination Area and the Traversable network.
To bridge this gap. an Average Overlay can be used. The buffering effect of an Average Overlay allows for "jumping" from the Destination Area and the Traversable network.
Reopen the list of Areas.
Add a new Area to the Project.
A new Area is now added, and selected in the left panel.
Its details are displayed in the right panel.
At the bottom of the right panel, click on "Adjust Area" to start manually drawing it in the Project map.
Draw it in the location of a point of interest such as a shop, sports-centre, cultural facility or other recreational destination. Draw it such that it is approximately a point-marker within a building without extending beyond its walls.
When drawn in properly, click on "Apply Selection".
In the right panel, switch to the Attributes tab.
At the bottom of the right panel's list of Attributes, fill in the form for a new Attribute with the following input:
- Name: DESTINATION_FACILITY
- Values: 1
This will now serve as the marker for a Point of Interest.
Open the Travel Distance Overlay Configuration Wizard, and progress to the step regarding Destination Areas.
Opt to select new Destination Areas based on an Attribute.
Change the dropdown to "DESTINATION_FACILITY", the Attribute added to the newly created Area.
Finish and exit the wizard, and recalculate the Overlay.
Notice that with this Destination Area drawn as it is, it only effectively highlights the location where the Destination lies, but the calculation does not traverse the potential routes away from it.
Add an Average Overlay.
A new Average Overlay is now added, and selected in the left panel.
Its details are displayed in the right panel.
Set the input layer to "Attribute Max Value"
Set the cell averaging distance to 5 meters.
Set the Attribute to "DESTINATION_FACILITY".
Open the Average Overlay's Configuration Wizard.
Continue to the "Operator" step.
Select the "MAX" value operator.
Close the Configuration Wizard, and recalculate the Project.
Take notice of the results in the Average Overlay. Although the source data (the Area) is effectively a point, the Average Overlay extends or buffers the data automatically. Because the operator is set to MAX rather than AVG, the "high" 1 value is used everywhere in the relevant circle.
Reselect the Travel Distance Overlay.
Open the Travel Distance Overlay's Configuration Wizard.
Continue to the "Destination Grid" step.
Opt to use a Grid Overlay as input for destinations.
As input Overlay, set the Average Overlay created previously.
Take note of the "Destination threshold". Cells in the input Overlay with values at or above this threshold are considered (part of) destinations to calculate travel distances to.
Close the configuration wizard.
Recalculate the Project.
Notice that now, rather than the smaller drawn Area resulting in only a highlighting of the direct environment of the point of interest, the larger highlighted area of the Average Overlay is used, touching the traversable network and as such creating a proper Travel Distance calculation.
Note that if you do not see this result yet, the most likely cause is the Average Overlay is using an "Averaging Distance" which is too low to touch the traversable network. If neccesary, increase the averaging distance and recalculate again.
With the possibility to connect Grid Overlays to the Travel Distance Overlay to define destinations, increasingly more complex inputs can be created, including the ability to fully calculate destinations on-the-fly.
Assignments
- Ensure you have the following Overlays:
- An Average Overlay highlighting the "DESTINATION_FACILITY", with an Averaging Distance of 0.
- A Combo Overlay, using both that Average Overlay as a Grid Input as well as a "LEISURE_CATEGORY_WEIGHT" as an Attribute Input. Set the formula to "GT(ADD(A,@A),0)"
(Check both inputs and if either of them exist, give an output) - A second Average Overlay which takes the Combo Overlay as input, with an averaging distance sufficient to reach the traversable network, and the operator (which ahs to be set via the Configuration Wizard) set to "MAX".
- Ensure that second Average Overlay is the destinations prequel of the Travel Distance Overlay. Recalculate the Project.
- Verify that you now see both the DESTINATION_FACILITY location, as well as any Buildings of the Leisure Categoery, are used as destinations for the Travel Distance Overlay's calculations.
Expanded modalities for the Travel Distance calculation
The routes which can be traveled across as part of the Travel Distance Overlay calculation are known as "traversables". By default, the Travel Distance Overlay only considers roads for cars to be traversable. The exact order of logic is that the Travel Distance Overlay is set to look for the car modality, and when any given Building has an amount of cars traveling over it, that Building qualifies. Cars are the default modality because there is generally a lot of unambiguous information on where cars exist and are or are not allowed.
The Travel Distance Overlay is capable of looking for different modalities insead of (or complementary to) cars. However, this will additional configuration to properly determine which kinds of Buildings are traversable for that mode of travel.
Open the Function Values window.
This window allows for configuring the default values and properties of Buildings, including the amount of traffic for various modes of travel.
At the top of the window, set the "Category Filter" to the ROAD Category.
Next, set the "Group Filter" to OTHER_TRAFFIC.
These filters ensure the oveview is a compact overview for exactly the values to be edited.
The default overview of Functions does not immediately show all possible Functions. More often than not, Functions should be explicitly added to this overview so they can be edited.
At the bottom of the Function Values window, find the "Add" Option for Functions.
A Function Selection window will open.
Switch to the Roads category, and select all Functions in that category.
Click on "Select" to confirm the selection.
The Functions are now added to the overview.
For all Functions on which pedestrians could travel, set the "Pedestrians / Hour" to at least 1.
For all Functions on which bicycles could travel, set the "Bicycles / Hour" to at least 1.
Change the Category filter to "INTERSECTION", again add all Functions of that category, and configure them with the appropriate "Pedestrians / Hour" and "Bicycles / Hour" vales.
Change the Category filter to "BRIDGE", again add all Functions of that category, and configure them with the appropriate "Pedestrians / Hour" and "Bicycles / Hour" vales.
When all changes have been made, close the Function Values window.
Next, the Travel Distance Overlay can be modified so that it is focussed specifically on those modalities.
Open the Travel Distance Overlay's Configuation Wizard.
Continue to the step regarding Traffic Types.
Ensure Pedestrians and Bicycles is checked. Ensure Cars and all other options are unchecked.
Close the Configuration Wizard.
Recalculate the Project.
The travel distance results are now different, more closely alligned with the routes for pedestrians and bicyclists.
This result can still be improved further. What the calculation does now is consider all pedestrian routes and bicycle routes as "traversable", meaning that who- or whatever is traveling can freely travel on both. A more proper calculation requires looking at pedestrian routes and bicycle routes separately.
Select the Travel Distance Overlay in the left panel.
At the bottom of the left panel, click on "Duplicate".
There is now a second Travel Distance Overlay.
With the first Travel Distance Overlay selected in the left panel, find the "Name" input in the right panel.
Rename this Overlay to "Travel Distance (Pedestrians)".
Open the Travel Distance Overlay's Configuation Wizard.
Continue to the step regarding Traffic Types.
Ensure only Pedestrians is checked. Ensure Bicycles and all other options are unchecked.
Close the Configuration Wizard.
With the second Travel Distance Overlay selected in the left panel, find the "Name" input in the right panel.
Rename this Overlay to "Travel Distance (Bicycles)".
Open the Travel Distance Overlay's Configuation Wizard.
Continue to the step regarding Traffic Types.
Ensure only Bicycles is checked. Ensure Pedestrians and all other options are unchecked.
Close the Configuration Wizard.
Recalculate the Project.
The travel distance results are now separated, showing distinct results for pedestrians and bicyclists.
Note that there may be unintended gaps in the network, preventing the travel distances from propagating properly. For now, if any propagation is visible (especially when the results between the two modalities are different), the results are sufficient.
Assignments
- Modify the Travel Distance Overlays' settings so that bicycles can travel twice as far as pedestrians.
- Add a Combo Overlay, with the following configuration:
- Input A: Travel Distance (Pedestrians)
- Input B: Travel Distanve (Bicycles)
- Formula: ADD( MUL(GTE(A,0), 1), MUL(GTE(B,0), 2) )
- Legend: 0 = Nothing, 1 = Pedestrians, 2 = Bicycles, 3 = Both.
Advanced traversables for the Travel Distance calculation
The results of the Travel Distance Overlay are strongly affected by the traversable network. Another benefit of the network of roads and cars is that these datasets usually have a good connective coverage, while pedestrian routes or bicycle paths can commonly be interrupted by road networks. In addition, there can be more kinds of routes allowed for some modalities, such as bicycles which could also travel on roads for cars as long as the maximum allowed speed on that road is low enough.
Out-of-the-box, the Travel Distance Overlay allows for looking directly at the values of Buildings for modes of travel. But like for destinations, the traversables can instead also be determined through a prequel. This allows for great flexibility both to both bridge the gap between the structure of data and the required input for a calculation, but also the on-the-fly additional calculation of additional potential routes.
The first step is to create an Overlay showing where the network for pedestrians exists.
Add an Combo Overlay.
A new Combo Overlay is now added, and selected in the left panel.
Rename it to "Pedestrian network"
In the right panel, switch to the "Inputs" tab.
Ensure the input layer is set to "BUILDINGS".
Set Attribute input A to "NUM_PEDESTRIANS".
Switch back to the "General" tab.
Set the formula to "GT(@A,0)"
Recalculate the Project.
This Overlay now highlights the locations of the pedestrian network.
Next, an Average Overlay can be used to buffer the routes to bridge the gaps.
Add an Average Overlay.
A new Average Overlay is now added, and selected in the left panel.
Rename it to "Pedestrian network (buffered)"
Set the input layer to "Grid Overlay"
Set the cell averaging distance to 5 meters.
Set the input Grid Overlay to the previously created Combo Overlay.
Open the Average Overlay's Configuration Wizard.
Continue to the "Operator" step.
Select the "MAX" value operator.
Close the Average Overlay's Configuration Wizard.
Recalculate the Project.
Inspect the buffered pedestrians network, and check whether there are any significant gaps left in the network. If so, increase the cell averaging distance a little bit until the gaps are resolved.
Finally, this new buffered network can be used as the traversable network for the Travel Distance Overlay for pedestrians.
Select the Travel Distance Overlay in the left panel.
Open the Travel Distance Overlay's Configuration Wizard.
Continue to the "Traversable Grid" step.
Opt to select a Grid Overlay as input for traversables.
Select the "Pedestrian Network (Buffered)"
By setting a traversable prequel, the settings for the traffic types are automatically disregarded.
Close the Configuration Wizard.
Recalculate the Project.
Notice the pedestrian travel distances now cross the gaps that they previously did not.
This setup could have also been realized without using the Combo Overlay, but the Combo Overlay allows for more kinds of surfaces to be defined and combined into a total allowed network for pedestrians. By directly using a Combo Overlay for this setup, it becomes easy to add more inputs in the future.
Assignments
- Create the same traversables setup for bicycles, with a Combo Overlay for the inputs, and an Average Overlay for buffering. Ensure that, to start with, the Combo Overlay only takes into account NUM_BICYCLES.
- Ammend the Combo Overlay for the bicycles network to also take into account roads with low-speed car traffic. Use the following extra settings in the Combo Overlay:
- Attribute Input B: NUM_CARS
- Attribute Input C: TRAFFIC_SPEED
- Formula: OR( GT(A,0), AND( GT(B,0),LTE(C,30) )
Filtering for relevant sources
With a Travel Distance Overlay calculation set up, the result is the locations where it is possible to travel, as well as a [[buffer around those reached locations to highlight the objects in that range (rather than only the parts of the network itself.
The intent of that buffer is to easily create follow-up calculations, filtering or classifying relevant objects.
The most common use-case for these features is to create insight in whether people have access to particular facilities without having to travel too far. It can vary whether the focus is on specifically people in residences, or whether it is also relevant to take into consideration commercial or public buildings.
Regardless of the exact type of Building to consider, the way to build up these different use-cases is the same, and somewhat mirrors how the destinations and the traversables have been set up as well.
Add an Combo Overlay.
A new Combo Overlay is now added, and selected in the left panel.
Rename it to "All Buildings"
In the right panel, switch to the "Inputs" tab.
Ensure the input layer is set to "BUILDINGS".
Set Attribute input A to "SOLID".
Switch back to the "General" tab.
Set the formula to "GT(@A,0)"
Add another Combo Overlay.
Rename it to "Buildings within traversable distance"
Set Input A to "Buildings".
Set Input B to "Travel Distance (Pedestrians)".
Set the formula to "IF(EQ(A,0),NO_DATA,GTE(B,0))"
Switch to the "Legend" tab, and activate the "Custom Legend"
Remove all entries (if any) and add 2 new ones.
Change one of the legend entries as follows:
- Value: 0
- Color: Red
- Text: Out of range
Change the other legend entry as follows.
- Value: 1
- Color: Green
- Text: In range
Recalculate the Project.
The result is an Overlay which shows which buildings are in range of the indicated destinations.
Tutorial completed
Congratulations. You have now completed this tutorial. In it, you have learned how to create a Travel Distance Overlay, and configure it with flexible inputs to fine-tune its calculations..