Isochrones are unique shapes calculated by travel time. The below example, shows where is reachable within 30 minutes driving from the centre of Brighton, UK.
Isochrone analysis can be useful in planning, logistics and office relocation. However, isochrones can be confusing. Here’s a guide on how to analyse an isochrone and how to understand the weird and wonderful shapes that are often created.
Islands on the map
An isochrone shape is dependent on the maximum time that the user wishes to travel and their preferred mode of transport. The example below shows where can be reached by public transport from the centre of London in 30 minutes.
The resulting isochrone shape has island locations that are reachable. For example, from the below zoomed in the image you can see that Finsbury Park, Seven Sisters and Walthamstow are reachable within 30 minutes, but that Haringey and Stamford Hill are not, despite being closer in terms of distance.
This is because the isochrone is calculated using public transport data and the Victoria line passes through these areas.
So, the user would be able to reach the locations on this line, including Finsbury Park, Seven Sisters and Walthamstow. However, the places in between these locations aren’t as easy to reach, which is why islands are formed.
Making multiple shapes on one map
Layering isochrones on a single map means you can compare how much further you could reach if you spend longer travelling. The images below use the free TravelTime maps tool and show where's reachable within 30 minutes, 45 minutes and 60 minutes of central London by public transport.
Looking more closely at a section of the map, you can see that with a maximum travel time of 30 minutes (the red isochrone shape), a user could reach as far as Wembley.
Increasing the travel time to 45 minutes (the blue isochrone shape) allows the user to reach all the way out to St. Albans.
This is because there is a fast train line connecting St. Albans to London, St. Pancras in 32 minutes.
The user could then travel on the London Underground into the centre of London.
This type of isochrone analysis can be useful when assessing staff travel times for office relocation, for example. You can also create a distance matrix to analyse multiple staff travel times in relation to multiple potential office locations. To find out more, get in touch.
The TravelTime platform radius map tool allows users to measure the distance from a starting point. The example below shows a 10 miles radius distance from central London.
The problem with radius distance is that it assumes the user travels as the crow flies. When in reality, there are many factors that affect journey time, such as time of day and mode of transport. This is where isochrone analysis becomes useful.
The example below shows the comparison of the 10-mile radius to the user travelling for 55 minutes by public transport.
The radius map tool provides an analysis for the user, as shown below.
The analysis states that 31% of the radius is not reachable within 55 minutes by public transport and that 12% of the areas that are reachable in 55 minutes fall outside of the radius. This means that there are locations within 10 miles that are not reachable within 55 minutes. There are also locations outside the 10 miles that could be reached within this time period, but these would not appear on a radius distance search. In short, 31% of the results on the radius distance search are irrelevant and 12% of the locations are missed opportunities as they are never shown to the user when searching by distance.
The higher the % of places not reachable in the radius, the poorer the transport connections are within the area. This suggests public transport connectivity can be improved. However, if there is a large % that is reachable outside, it shows that there are some fast transport connections that can enable travellers to go further than expected.
Below is a similar example using driving.
Gaps in the isochrone shape
A travel time map shows the user where they could reach within their specified travel time and mode of transport. This means that if there is an area that is not reachable within the travel time limit, the shape will leave a gap.
The below example shows where is reachable within 60 minutes by public transport from an address in Glasgow.
Looking more closely at an area of the map, you can see a gap in the shape.
Identifying public transport black spots can be important in planning and logistics as some locations appear to be close, but in reality, are hard to reach.
The introduction of holes into an isochrone can make the shape more complex to understand as it will mean isochrone shapes can’t expand out like a heat map. For example, one of the earliest isochrones shows that the user can reach anywhere in Europe within 10 days and ignores that some parts may be remote, therefore more difficult to reach.
Isochronic Passage Chart Francis Galton 1881
Finding mutually accessible locations
Isochrone analysis can be useful when trying to find out a location that is equidistant from two separate start points. In this example the user to create two isochrone shapes and discover where they overlap. The example below shows:
- Red isochrone - Where is reachable within 60 minutes from central London, travelling by public transport
- Yellow isochrone - Where is reachable within 45 minutes from St. Albans, travelling by public transport
- Red and yellow numbered pins - the hotels that are situated within each isochrone shape. These are also listed on the left-hand side
If the user wanted to find out which hotels could be reached within both travel times, they could click the ‘filter intersection’ button.
The map would then highlight the areas where the isochrones intersect and show the relevant results.
This type of isochrone analysis can help to inform decision making, including property purchases, meeting locations and office relocations. On a larger scale, retailers can plot thousands of their own store locations, competitor locations and customer locations to see which areas are ripe for development.
Staff travel time heat mapping
It’s also possible to overlay many shapes and perform analysis on these. Here is an example of an office relocation analysis. The first step (not shown) calculates hundreds of isochrone areas, creating a shape that shows where each employee could reach within 45 minutes. These shapes are combined together to see which locations are best.
Area colour % Of employeesArea colour % Of employeesYellow100% of employees can reach in 45 minutesPink80% of employees can reach in 45 minutesBlue60% of employees can reach in 45 minutesGreen40% of employees can reach in 45 minutesGrey20% of employees can reach in 45 minutes.