How to define catchment area in Sloc Local
Catchment areas represent geographic zones, defined by time or distance, that the vast majority of a site's customers are willing to travel for that site's services. Typically, authorities set this to an area covering the closest 80% of customers to each site. In practice, catchment areas are often derived from precedent of similar merger control cases when such data is difficult to source.
As the pragmatic proxy for local market boundaries, the findings of competitive assessments hinge on catchment area definitions. Sloc Local makes it a breeze to flex and test different catchment area scenarios on your specific local merger to give you confidence in your results from the moment they run and to be prepared for any outcome.
How to run a local merger analysis scenario
With your site data prepared and geocoded, you are all set to simply specify the specific catchment area scenarios you wish to test and visualise your results. You can customise this using a combination of distance or time-based methods, mode of transport, and catchment size.
This guide explains the available catchment parameters, how they work, and how to configure them to strike the right balance between realism and performance.
Catchment type
Choose the type of catchment area that best reflects your case context:
Catchment type | Description | Catchment shape | Run speed |
|---|---|---|---|
Straight-line | Circular catchments using “as-the-crow-flies” distance (in kilometres) | Circular catchment. | Fastest |
Street-wise | Distance-based catchments using optimal routes via roads and paths (in metres) | Isoquant catchment: Covers a set distance (e.g. 5,000m), around the central Party site. | Slower |
Travel-time | Time-based catchments using optimal routes via roads and paths (in minutes) | Isochrone catchment: Covers a set travel time duration (e.g. 15 minutes), around the central Party site | Slowest |
Straight-line catchments are very fast and useful for rough estimates, but don't account for real world geographic features such as rivers, busy/winding roads, or difficult terrain. Street-wise and travel-time catchments align with the 'gold standard' approach - accurately representing with real world travel - but are much slower and more difficult to calculate.
Method of transport (Not applicable for straight-line)
Choose how people are assumed to travel to sites:
Walking
Cycling
Driving
Each mode accounts for the different optimal routes and speeds associated with that method of transport on that specific route. Typically, the method of transport chosen aligns with the approach customers typically take for travelling to sites in the industry in question.
🧠 Note: Driving scenarios require more processing time and support additional features like traffic modelling based on Departure time.
Departure time (Driving only)
For driving scenarios, you must also specify a departure time to take traffic and road conditions into account.
Supports past or future times
Reflects real-world delays and closures where relevant
When no specific departure time is selected, it defaults to 10:30 AM on Tuesday, 25th March 2025.
The departure time chosen should align closely with the most representative time that customers travel to sites in the industry in question.
Catchment size limits
Each method has its own maximum supported catchment size:
Catchment type | Unit | Max size |
|---|---|---|
Straight-line | Kilometres (km) | Up to 100 km |
Street-wise | Metres (m) | Up to 100,000 m |
Travel-time | Minutes (min) | Up to 60 min |
Choose a size that reflects a realistic travel range for the market being analysed.
Performance considerations
The more complex the configuration, the longer the scenario may take to run. Key factors affecting run time include:
Number of local markets examined (Party 'centroids')
Size of catchments
Use of complex, optimal street-wise or travel-time methods
Driving scenarios (which must account for traffic)
🧠 Tip: Sloc Local caches previously calculated routes. Running similar scenarios will be significantly faster the second time around, as Sloc avoids reprocessing the same paths.