Glossary

Access Index (AI): This index is one of the stages in calculating PTAL values. The full calculation method is described in our connectivity assessment guide.

Accessibility: A station or a service is accessible if it is suitable for people with a range of needs, such as with wheelchairs or heavy shopping. In some places, the term accessibility is used to describe more generally how good transport is in different areas. We use the term Connectivity for this, to avoid confusion.

AM Peak: The hours in the morning when the transport system is very busy. We consider the three-hour period from 07:00 to 10:00 to represent the AM peak.

Areas for Intensification: Areas identified in the London Plan as having high potential for the development of more homes and workplaces.

Base Year: The year that represents the current state of the transport system. 2011 is used as the base year in WebCAT. We normally do not use the current year but a relatively recent year for which we have a sufficient amount of data. The base year is used as a consistent baseline for different types of analysis.

Between Peak Times: The time during a weekday when the transport system is less busy than in the peak. We consider the six-hour period from 10:00 to 16:00 to represent this period. This period is also sometimes called the inter-peak period.

Catchment: In WebCAT, a catchment area contains all the places that can be reached within a specified travel time from a specified place. We often calculate the population or number of workplaces within the catchment area. Catchment analysis is not included in the first release of WebCAT but will be included later.

Census: A very large survey where information is collected from all the people that live in the country. The last census in England was undertaken in 2011. Information from the census is used in various parts of WebCAT.

Census Output Areas (COAs): A set of boundaries that splits Greater London into 25,053 zones for the purpose of analysis.

Connectivity: If it is easy to travel to or from a place then it has a good level of connectivity. PTAL and TIM are two measures of connectivity.

District centres: One of the categories of town centres which we used for connectivity assessment. District centres provide goods and services for local communities. They are accessible by public transport, walking and cycling, and typically contain 10,000-50,000m² of retail floorspace.

DLR: Docklands Light Railway

Economically Active Population. The number of people that are employed or are actively looking for work. This is derived from population forecasts published by the Greater London Authority.

Employment data: Information on the number of workplaces in a selected area. The information on WebCAT comes from the Greater London Authority, as published in 2012, or forecasts created from this data for future years.

Equivalent Doorstep Frequency: This is one of the stages in calculating PTAL values. The full calculation is described in the connectivity assessment guide.

Frequency: The number of public transport journeys per hour on one specific route, or at one specific place. Frequency is often measured in vehicles per hour or departures per hour.

Grid: A series of points with fixed distances between them. PTAL values in WebCAT are calculated in advance for a grid of points that covers London.

Headway: The time between two arrivals of a public transport service. If the frequency of a service is 6 per hour then the headway is 10 minutes.

Households: Information on the number of households in a selected area. The information on WebCAT comes from the Greater London Authority, as published in 2012, following the 2011 census, or forecasts created from this data for future years.

International centres: One of the categories of town centres which we use for connectivity assessment. International centres are London's principal retail destinations, with a wide range shopping options and very good public transport connectivity.

Key locations: Different types of locations which are relevant for catchment analysis. They may be town centres, schools or colleges, or locations of health services.

London Plan: A document published by the Greater London Authority which contains the overall strategic plan for London for the period until 2031, including economic, environmental, transport and social topics.

Lower Super Output Areas (LSOAs): A set of boundaries that splits Greater London into 4,835 zones for the purpose of analysis.

Major centres: One of the categories of town centres which we use for connectivity assessment. Major centres generally contain over 50,000m² of retail floorspace and serve people within the Borough they are in. They often have significant employment, leisure, service and civic functions.

Metropolitan centres: One of the categories of town centres which we use for connectivity assessment. Metropolitan centres generally contain at least 100,000m² of retail floorspace and several people from several Boroughs, as well as visitors from the wider south east of England. These centres generally have very good connectivity and significant employment, service and leisure functions.

Mode: In WebCAT we currently define a mode as one of the following options: all public transport modes; bus only; or step-free services. Note that bus services are included in all three categories.

Model: Models (or transport models) are computer tools that help us estimate how the transport system will work, and how people will travel, in future scenarios. A range of our transport models are described on the Strategic transport & land-use models page.

Opportunity Areas: Areas identified in the London Plan as suitable for large-scale development to provide high numbers of new homes and workplaces.

Population data: Information on the number of residents in a selected area. The information on WebCAT comes from the Greater London Authority, as published in 2012, following the 2011 census, or forecasts created from this data for future years.

PM Peak: The hours in the afternoon or early evening when the transport system is very busy. We consider the three-hour period from 16:00 to 19:00 to represent the PM peak.

Population Aged 75+: The total population aged over 75 in a selected area. This is derived from population forecasts published by the Greater London Authority.

Population at Pensionable Age: The total population at an age when pension is likely to be their main income. This is derived from population forecasts published by the Greater London Authority.

Population at Working Age: The total population at an age in which they can normally work. This is derived from population forecasts published by the Greater London Authority.

PTAL: Public Transport Access Level. This is a measure of connectivity to the public transport network. The method used to calculate PTAL is described in the connectivity assessment guide.

Scenario: A version of the transport system which may or may not happen. London's transport system, with all the streets and routes that exist today, are one scenario. London's transport system in the year 2021, including for example the Crossrail route, are another possible scenario. For transport planning we often define many scenario and do separate connectivity assessment for each one.

Standard wait time: This is one of the stages in calculating PTAL values. The full calculation method is described in the connectivity assessment guide.

Step-free services: Public transport services that can be used also by people with limited mobility, such as wheelchair users. Step-free services are defined in WebCAT as a separate mode, in the mode drop-down menu for TIM.

TIM: An acronym for Time Mapping which is one of the measures of connectivity that can be assessed with WebCAT. The method used to calculate PTAL values is described in the connectivity assessment guide.

Time of Day: Part of the day for which we have estimates travel time. Times of Day that can be checked on WebCAT with TIM are the AM Peak, Between Peak Times and PM Peak.

Total Access Time: This is one of the stages in calculating PTAL values. The full calculation method is described in the connectivity assessment guide.

Town Centres: A series of central locations defined by the Greater London Authority. We often use these locations in our connectivity assessment since they represent places that people often go to.

WebCAT: Web-based Connectivity Assessment Toolkit. We introduced this in 2015 for the use of professional planners.

Zone: When we do analysis using models, we split the area of London into zones, and we calculate travel times from each zone to each zone. One zone typically contains a few hundreds of buildings.

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