Catchment Area

Catchment Areas show how far people can travel within a certain travel time or distance, using one or more modes of transport.

1. Explanation

Based on the specified starting point(s), maximum travel time or distance, and mode(s) of transport, Catchment Areas visualize the extent of accessibility. This is calculated using real-world data and provides useful insights into the quality, density, and extensiveness of an area's transport network.

Furthermore, the catchment area can be intersected with spatial datasets, such as population and POI data. This allows you to assess - for example - how many POIs can be reached from a certain location and therefore identify what share of inhabitants has access to important amenities within a specific travel time.

Hint

You might know this feature from our previous software versions under the terms Single-Isochrone and Multi-Isochrone. With the release of GOAT version 2.0, we combined these two indicators in the same flow and enriched it with further calculation options.

info

Catchment areas are available for certain regions. Upon selecting a Routing type, GOAT will dynamically display a geofence for supported regions. For Walk, Bicycle, Pedelec, and Car, the geofence reaches more than 30 European countries:

For Public Transport, the geofence reaches all of Germany:

In case you need to perform analysis beyond this geofence, feel free to contact the Support and we will check what is possible.

2. Example use cases

• Which amenities can be reached from a certain point in a 15-minute walk?
• How many inhabitants have access to a supermarket within 10 minutes of cycling?
• What share of the population has a general practitioner (GP) within 500m distance?
• How big is the catchment area of a workplace by car vs. by public transport? How many employees live within these catchment areas?
• How well are kindergartens currently distributed across the city? In which districts are there accessibility deficits?

3. How to use the indicator?

1

Click on Toolbox .

2

Under the Accessibility Indicators menu, click on Catchment Area.

Routing

3

Pick for which Routing Type you would like to calculate a catchment area.

Configuration

Walk

Walk

Considers all paths accessible by foot.

Hint

For further insights into the Routing algorithm, visit Routing/Walk.

4

Pick if you like to calculate the catchment area based on time or distance.

Time

Time

5

Set the configurations for Travel time limit, Travel speed, and Number of breaks.

Hint

For defining which travel time limits are suitable for which amenity, the "Standort-Werkzeug" of the City of Chemnitz can provide helpful guidance.

Advanced Configurations

Per default, the catchment areas are calculated in polygon shape. In case you want to adjust that, you find further options in the advanced configurations.

6

Click on options button . Here you can select the Catchment area shape. You can choose between Polygon, Network and Rectangular Grid.

Distance

Distance

5

Set the configurations for Travel distance and Number of breaks.

Hint

For defining which travel distances are suitable for which amenity, the "Standort-Werkzeug" of the City of Chemnitz can provide helpful guidance.

Advanced Configurations

Per default, the catchment areas are calculated in polygon shape. In case you want to adjust that, you find further options in the advanced configurations.

6

Click on options button . Here you can select the Catchment area shape. You can choose between Polygon, Network and Rectangular Grid.

Bicycle/Pedelec

Bicycle/Pedelec

Considers all paths accessible by bicycle. This routing mode takes into account the surface, smoothness, and slope of streets while computing accessibility. For Pedelec, slopes are considered with a lower impedance than for standard bicycles.

Hint

For further insights into the Routing algorithm, visit Routing/Bicycle. In addition, you can check this Publication.

4

Pick if you like to calculate the catchment area based on time or distance.

Time

Time

5

Set the configurations for Travel time limit, Travel speed, and Number of breaks.

Hint

For defining which travel time limits are suitable for which amenity, the "Standort-Werkzeug" of the City of Chemnitz can provide helpful guidance.

Advanced Configurations

Per default, the catchment areas are calculated in polygon shape. In case you want to adjust that, you find further options in the advanced configurations.

6

Click on options button . Here you can select the Catchment area shape. You can choose between Polygon, Network and Rectangular Grid.

Distance

Distance

5

Set the configurations for Travel distance and Number of breaks.

Hint

For defining which travel distances are suitable for which amenity, the "Standort-Werkzeug" of the City of Chemnitz can provide helpful guidance.

Advanced Configurations

Per default, the catchment areas are calculated in polygon shape. In case you want to adjust that, you find further options in the advanced configurations.

6

Click on options button . Here you can select the Catchment area shape. You can choose between Polygon, Network and Rectangular Grid.

Car

Car

Considers all paths accessible by car. This routing mode takes into account speed limits and one-way access restrictions while computing accessibility.

Hint

For further insights into the Routing algorithm, visit Routing/Car.

4

Pick if you like to calculate the catchment area based on time or distance.

Time

Time

5

Set the configurations for Travel time limit and Number of breaks.

Advanced Configurations

Per default, the catchment areas are calculated in polygon shape. In case you want to adjust that, you find further options in the advanced configurations.

6

Click on options button . Here you can select the Catchment area shape. You can choose between Polygon, Network and Rectangular Grid.

Distance

Distance

5

Set the configurations for Travel distance and Number of breaks.

Advanced Configurations

Per default, the catchment areas are calculated in polygon shape. In case you want to adjust that, you find further options in the advanced configurations.

6

Click on options button . Here you can select the Catchment area shape. You can choose between Polygon, Network and Rectangular Grid.

Public Transport (PT)

Public Transport (PT)

Considers all locations accessible by public transport. This routing mode considers inter-modal transfers including access to and from stations.

Hint

For further insights into the Routing algorithm, visit Routing/Public Transport.

4

Select the Public transport modes you want to analyze (Bus, Tram, Rail, Subway, Ferry, Cable Car, Gondola and/or Funicular).

5

Set the configurations for Travel time limit, Number of breaks, Day (Weekday, Saturday or Sunday) and Time period (Start Time and End Time).

Hint

For defining which travel time limits are suitable for which amenity, the "Standort-Werkzeug" of the City of Chemnitz can provide helpful guidance.

Advanced Configurations

Per default, the catchment areas are calculated in polygon shape. In case you want to adjust that, you find further options in the advanced configurations.

6

Click on options button . Here you can select the Catchment area shape. You can choose between Polygon, Network and Rectangular Grid.

Polygon

Polygon

• It is the geometric representation of the catchments.
• Provides an easy-to-understand visualization of the catchment area.
• One polygon is produced for each step.

NOTE

If you enable Polygon Difference, only the "incremental" (or differential) polygon will be created for each step, but if you disable Polygon Difference, a "full" polygon will be created for each step (including the areas covered by all previous steps).

Network

Network

• It is a street-level representation of the catchments.
• Enables easy correlation to actual streets and their accessibility within the catchment area.
• Fine-grained detail compared to the other catchment types.

Rectangular Grid

Rectangular Grid

• It is a grid cell-based representation of the catchments.
• Appears similar to a “heatmap” visualization, however, differs conceptually & computationally (this represents egress from a specified origin to various other locations while heatmaps represent access from various locations to a specified destination).

Starting Points

7

Select the Starting point method to define how you like to define the starting point(s) for the catchment areas. You can either Select on map or Select from layer.

Select on Map

Select on Map

8

Choose Select on map. Select the starting point(s) by clicking on the respective location(s) in the map. You can add as many starting points as you like.

Select From Layer

Select From Layer

8

Click on Select from layer. Select the Point layer which contains the starting point(s) you like to use.

9

Click on Run. This starts the calculation of the catchment areas from the selected starting point(s).

Hint

Depending on the chosen settings, the calculation might take some minutes. The status bar shows the current progress.

Results

10

As soon as the calculation process is finished, the resulting layer(s) will be added to the map. The layer called "Catchment Area" contains the calculated catchments. If the starting points were created by clicking on the map, they will also be saved in a layer called "Starting Points".

If you click on a catchment polygon on the map, you will see further details in its attribute table. The attribute travel_cost shows the travel distance or time, depending on which unit you picked for the calculation. If you have selected travel time, the travel_cost will show the time in minutes. If you have selected distance, the travel_cost will show the distance in meters.

Tip

Want to style your catchment areas and create nice looking maps? See Styling.

4. Technical details

Catchment areas are isolines connecting all points that can be reached from one or more starting points within a certain time interval (called isochrones) or distance (called isodistance). Depending on the chosen travel mode, the according transport networks are used for the routing.

The catchment areas are dynamically created in the front end based on a travel time/distance grid. Therefore, catchment areas can be created fast and for different intervals on the fly.

Scientific background

From the scientific background, catchments are contour-based measures (also known as cumulative opportunities). They are valued for their easily interpretable results (Geurs and van Eck 2001; Albacete 2016), but have the drawback of not distinguishing between different travel times within the cut-off range (Bertolini, le Clercq, and Kapoen 2005), as it is done by heatmaps.

Visualization

The catchment shape is derived from the routing grid using the Marching square contour line algorithm, a computer graphics algorithm that can generate two-dimensional contour lines from a rectangular array of values (de Queiroz Neto et al. 2016). This algorithm transforms the grid from a 2D array to a shape to visualize or analyze. An illustration of 2D image processing is shown in the figure.

5. Further readings

Further insights into the catchment calculation and its scientific background can be found in this publication.

6. References

Albacete, Xavier. 2016. “Evaluation and Improvements of Contour-Based Accessibility Measures.” url: https://dspace.uef.fi/bitstream/handle/123456789/16857/urn_isbn_978-952-61-2103-1.pdf?sequence=1&isAllowed=y

Bertolini, Luca, F. le Clercq, and L. Kapoen. 2005. “Sustainable Accessibility: A Conceptual Framework to Integrate Transport and Land Use Plan-Making. Two Test-Applications in the Netherlands and a Reflection on the Way Forward.” Transport Policy 12 (3): 207–20. https://doi.org/10.1016/j.tranpol.2005.01.006.

J. F. de Queiroz Neto, E. M. d. Santos, and C. A. Vidal. “MSKDE - Using Marching Squares to Quickly Make High Quality Crime Hotspot Maps”. en. In: 2016 29th SIBGRAPI Conference on Graphics, Patterns and Images (SIBGRAPI). Sao Paulo, Brazil: IEEE, Oct. 2016, pp. 305–312. isbn: 978-1-5090-3568-7. doi: 10.1109/SIBGRAPI.2016.049. url: https://ieeexplore.ieee.org/document/7813048

https://fr.wikipedia.org/wiki/Marching_squares#/media/Fichier:Marching_Squares_Isoline.svg

Majk Shkurti, "Spatio-temporal public transport accessibility analysis and benchmarking in an interactive WebGIS", Sep 2022. url: https://www.researchgate.net/publication/365790691_Spatio-temporal_public_transport_accessibility_analysis_and_benchmarking_in_an_interactive_WebGIS

Matthew Wigginton Conway, Andrew Byrd, Marco Van Der Linden. "Evidence-Based Transit and Land Use Sketch Planning Using Interactive Accessibility Methods on Combined Schedule and Headway-Based Networks", 2017. url: https://journals.sagepub.com/doi/10.3141/2653-06

Geurs, Karst T., and Ritsema van Eck. 2001. “Accessibility Measures: Review and Applications.” RIVM Report 408505 006. url: https://rivm.openrepository.com/handle/10029/259808