This has been traditionally called 'accessibility analysis'. We now often use the word 'accessibility' when discussing how suitable services are for a wide range of users, for example wheelchair users. As a result, TfL will now use the term 'connectivity assessment' for the process of estimating how well a development site is served by public transport. (Find out how TfL approaches transport accessibility.)

The London Plan and various other policy documents continue to use the term 'accessibility', because the distinction between these two terms is relatively new. Any reference we make to 'connectivity' should be read in this context. In some of these planning documents, 'accessibility' should be read to mean 'connectivity' if the context is broader than accessibility for users with different needs. We expect the difference in terminology to be reconciled when future versions of the relevant documents are published.


The most widely recognised way to measure connectivity to the public transport network in London is by using PTAL. This is an acronym for Public Transport Accessibility Level. To avoid confusion with the other meaning of 'accessibility', in the future we will define the acronym PTAL as Public Transport Access Level. It is worth noting however that all uses of PTAL by TfL or the Greater London Authority refer to the same indicator.

The PTAL value combines information about how close public transport services are to a site and how frequent these services are. The highest level of connectivity has a PTAL of 6b and the lowest has a PTAL of 0. For the policies in the London Plan, it is important to use connectivity indicators like PTAL because sites with better connectivity provide opportunities for development at higher densities and for sustainable development that reduces the need to travel by car.


You can check PTAL values for a specific area using our new Connectivity Assessment Toolkit, WebCAT. This replaces the web calculator used previously. It also includes new features such as PTAL values estimated for future scenarios based on suggested improvements to the transport network. The Time Mapping (TIM) feature of WebCAT also allows users to create maps that show how long it takes to travel to or from a selected location.

In WebCAT, PTAL is shown using a grid of squares that are 100m on each side, presented on top of a Google map of London. There are nearly 160,000 squares covering the whole of London. The PTAL value for each square is calculated at the centre of the square.

Information on how PTAL is calculated and presented is in our full connectivity assessment guide, available on the Planning with WebCAT page. The connectivity assessment guide also gives information on other complementary measures of connectivity and shows examples for their use.

Connectivity assessment should be discussed during the formal pre-application process. In addition, other tools are available from commercial software developers, which can be used to assess the level of connectivity around London.