The site analysis tool was built in collaboration with planning policy officers and allows users to understand the opportunity for sustainable travel in a given area. The tool uses the most up to date national datasets from Ordnance Survey, the National Health Service, Care Quality Commission, and Natural England to inform multi modal travel time analysis across a defined strategic area. The tool allows users to customise the facilities they wish to look at and the travel times they wish to prioritise and can be used in combination with our other overlays including custom user uploaded overlays to gain a better understanding of their area.
We call a particular category of facilities that you can analyse in this tool a metric. See the full list of available metrics in the appendix
Limitations
A later section details how the metrics are calculated, but a summary of the limitations of this tool can be found below:
- All data used for the basis for analysis is derived from third-party data.
- Where a third-party data provider does not provide a live data download, data is reflective of an update cycle based on that provider.
- The quality of third-party data is reflective of their own management and audit processes.
- OS data is derived gazetteer data managed by Local Authorities, therefore the accuracy and quality of building location data and categorisation of the use of buildings reflects recordings at source and cannot be altered or refined to a greater granularity.
- The analysis area is broken up into 500m grid squares for sampling. The program will look for a road within 250m of the centre of each square and take the nearest road point as the origin of the journey.
- The heatmap is an approximate visualisation of the underlying grid; by its nature, it may suggest values that fall outside of the source point’s original grid square.
- No account is currently taken for the quality of routes and existing infrastructure, thus while the map highlights the potential for sustainable travel it is not suggested to reflect the true nature of available routes.
- Driving times for cars are based on OpenStreetMap tags, with a constant value that makes no assumptions about traffic impacts.
- Bus times include wait times and are based on a typical Weekday morning arrival frequency and travel time
Counting the metrics
We begin by taking the target area and dicing it up into a grid with 500m divisions. This reduces the amount of points that have to be calculated, without severely impacting the resolution of the output visualisation. Every grid square is analysed in isolation, building isochrones from the centre for each travel mode. Our process for building isochrones is quite complex, see the technical brief for further detail. In the cases where the centre of a grid square does not lie on a road, we look in a 250m radius around it for a nearby place to start the route.
Once the isochrone has been generated, we draw a line around the area that can be reached at given intervals, i.e. the catchment area. These polygons can then be intersected with the metric sources, counting how many of each lie within.
Point features are counted when they fall within a catchment. Polygon features (for example, national parks) are counted once if any part of them intersect with the catchment.
Calculation modes
The tool has a number of modes to modify how the accessibility calculation is performed. These exist to fine tune the visualisation, for example if you are only concerned whether a facility can be reached, rather than how many of a given facility can be reached. These are controlled in the overlay configuration, under Analysis calculation.
Value type
The “value” of a metric can be one of two:
- count: the raw count of how many of the given facility can be accessed.
- existence: whether the facility can be accessed or not (i.e. count is greater than zero). If the facility can be accessed, a value of 1 is used; if not, 0.
Combination mode
This determines how the different modes of a metric are combined to give a total score.
Relative
The relative combination mode takes all modes into account. Each mode has a defined weight, which is normalised and multiplied by the value.
\[S = \frac{W_{\textrm{walk}}}{W_{\textrm{total}}}C_{\textrm{walk}} + \frac{W_{\textrm{cycle}}}{W_{\textrm{total}}}C_{\textrm{cycle}} + \frac{W_{\textrm{bus}}}{W_{\textrm{total}}}C_{\textrm{bus}} + \frac{W_{\textrm{car}}}{W_{\textrm{total}}}C_{\textrm{car}}
\]
Where:
- \(C_{\textrm{mode}}\) is the count of a given mode and time
- \(S\) is the total score for the location
- \(W_{\textrm{mode}}\) is the count of a given mode and time
Hierarchy
The hierarchy combination mode only takes into account the most accessible, non-zero value. That value is multiplied by the mode’s weight to give the score. The modes from most to least accessible are walk > cycle > bus > car.
\[S = W\cdot C\]Where:
- \(C\) is the count of the most accessible mode and time
- \(S\) is the total score for the location
- \(W\) is the count of the most accessible mode and time
Worked examples
Given a particular location, the following is true:
- There are 0 hospitals within 10 minutes’ walk, with a weight of 1
- There are 2 hospitals within 10 minutes’ cycle, with a weight of 0.8
- There is 1 hospital within 10 minutes’ on the bus, with a weight of 0.5
- There are 3 hospitals within 10 minutes’ drive, with a weight of 0.2
Relative count
The total weight of all the metrics, \(W_{\textrm{total}}\), is \(1 + 0.8 + 0.5 + 0.2\ = 2.5\).
The relative score is calculated as:
\[\frac{1}{2.5}\cdot0 + \frac{0.8}{2.5}\cdot2 + \frac{0.5}{2.5}\cdot1 + \frac{0.2}{2.5}\cdot2 = 1.08
\]
Relative existence
The total weight of all the metrics, \(W_{\textrm{total}}\), is \(1 + 0.8 + 0.5 + 0.2\ = 2.5\).
The relative score is calculated as:
\[\frac{1}{2.5}\cdot0 + \frac{0.8}{2.5}\cdot1 + \frac{0.5}{2.5}\cdot1 + \frac{0.2}{2.5}\cdot1 = 0.6
\]
Hierarchy count
The most accessible mode is cycle, so the score is calculated as:
\[2\cdot0.8 = 1.6\]Hierarchy existence
The most accessible mode is cycle, so the score is calculated as:
\[1\cdot0.8 = 0.8\]Generating the visualisation
There are two ways to visualise the accessibility of your area
- grid view shows the underlying grid that was used to sample points from the area
- heatmap uses the centroids of each grid square to produce a smoother, but less accurate representation
The colour at a particular point of the visualisation is picked from the user-defined scale. The maximum of the scale corresponds to the highest score across the entire study area
Appendix
Full list of metrics
This is a list of all the metrics available in the tool:
| Metric | Source | Acquisition detail |
|---|---|---|
| Allotments or community growing spaces | OS Greenspace | Where primary or secondary function is “Allotments Or Community Growing spaces” |
| Ambulance station | OS Addressbase Plus | Where classification is CX03 |
| Ancient woodland | Natural England – Ancient woodland | – |
| Bank or other financial service | OS Addressbase Plus | Where classification is CR01 |
| Bus shelter | OS Addressbase Plus | Where classification is CT02 |
| Cemetery or religious grounds | OS Greenspace | Where primary or secondary function is “Cemetery” or “Religious Grounds” |
| College | OS Addressbase Plus | Where classification is CE01 or CE01FE |
| Dentist | Care Quality Commission | Where “location type/sector” is “Primary Dental Care” and “Service user band – Whole population” is “Y” |
| Elderly care or nursing home | Care Quality Commission | Where “location primary inspection category” is “Residential social care” and “Service user band – Older people” is “Y” |
| Equipped children’s play space | OS Greenspace | Where primary or secondary function is “Play Space” |
| Fast food or takeaway outlet | OS Addressbase Plus | Where classification is CR10 |
| Fire station | OS Addressbase Plus | Where classification is CX02 |
| GP practice | NHS Digital | Where primary or secondary role is RO76 or RO96 |
| General retail | OS Addressbase Plus | Where classification is CR or CR08 |
| General use sports facility | OS Greenspace | Where primary or secondary function is “Other Sports Facility” |
| Hospital | Care Quality Commission | Where “location type/sector” is “NHS Healthcare Organisation”, “location primary inspection category” is “Acute hospital – NHS non-specialist”, “regulated activity – assessment or medical treatment for person “is “Y”, “regulated activity – termination of pregnancies” is “Y”, and “regulated activity – maternity and midwifery services” is “Y” |
| Library | OS Addressbase Plus | Where classification is CL03 |
| Local nature reserve | Natural England – Local nature reserves | – |
| Market | OS Addressbase Plus | Where classification starts with CR04 |
| National nature reserve | Natural England – National nature reserves | – |
| National park | Natural England – National parks | – |
| Nursery or creche | OS Addressbase Plus | Where classification is CE02 |
| Other retail services | OS Addressbase Plus | Where classification is CR02 |
| Petrol station | OS Addressbase Plus | Where classification is CR05 |
| Pharmacy | NHS Digital | Where primary or secondary role is RO181 or RO182 |
| Place of worship | OS Addressbase Plus | Where classification starts with ZW99 |
| Playing field | OS Greenspace | Where primary or secondary function is “Playing Field” |
| Police station | OS Addressbase Plus | Where classification is CX01 |
| Post office | OS Addressbase Plus | Where classification is CR02PO |
| Primary education | OS Addressbase Plus | Where classification is one of CE03, CE03FS, CE03IS, CE03JS, CE03MS, or CE03PS |
| Pub, bar or nightclub | OS Addressbase Plus | Where classification starts with CR06 |
| Public car park | OS Addressbase Plus | Where classification is CT03PP |
| Public hall or community building | OS Addressbase Plus | Where classification is CC04 |
| Public park or garden | OS Greenspace | Where primary or secondary function is “Public Park Or Garden” |
| Rail or bus station | OS Addressbase Plus | Where classification starts with CT08 |
| Religious meeting place | OS Addressbase Plus | Where classification is CC07 |
| Restaurant or café | OS Addressbase Plus | Where classification is CR07 |
| Secondary education | OS Addressbase Plus | Where classification is one or CE04, CE01HE, or CE04SS |
| University | OS Addressbase Plus | Where classification is CE05 |
| Youth or social club | OS Addressbase Plus | Where classification is CC04YR |