• In order to represent accessibility
information digitally, we have to break
down the real-life environment into its
discrete features (objects, elements) :
- Corridors, etc.
• Each object has a set of properties
(attributes) describing it from the viewpoint
- eg. a ramp has a particular slope
(inclination) and width that make it
(in)accessible for a wheelchair user
Outdoor objects and accessibility
for each type of object – outdoor or indoor
-‐ after creating (or finding) a digital element to represent a real-life
object, make note of its ID as well as values for its attributes
Objects in OpenStreetMap (OSM)
• OSM lets us create digital
representations of outdoor objects
• Real-life objects are represented in OSM
by using geometric elements:
- points (known as ‘nodes’ in OSM)
- lines (‘ways’), and
- areas (‘closed ways’)
• Each element can be described (‘tagged’)
to store info about attributes of the
OSM on smartphones
Desktop OSM: JOSM
• 1. Download current map data from
• 2. Edit map elements using satellite
imagery, GPS, field papers and notes as
well as using our knowledge of a place
• 3. Save changes to OpenStreetMap
Nodes in OSM
• Nodes in OSM are point elements.
• They define a single geospatial point,
using a latitude and longitude.
Ways in OSM
• Way is a general term for a series of
• They usually represent linear objects
(vectors), such as rivers or roads.
• Ways can also represent solid polygons
(areas), such as buildings or forests. In
this case, an area is a way whose first and
last node are the same – a closed way.
• Closed ways occasionally represent linear
loops, such as highway roundabouts,
rather than solid ('filled') areas.
Tags in OSM
• All elements have tags that describe the
objects that the elements represent in
• Tags are organized into keys and values.
The general form of a tag is key=value.
• Keys are categories of object properties,
such as Land Use for a closed way
representing a plot.
• Values specify keys, eg.
Example: representing steps (and ramps)
• After entering a line (‘way’ in OSM) to
represent the steps, we need to tag it
• highway=steps: “highway“ is a key describing
what kind of linear element the way is
• incline=20%: “incline” is a key to store the
• ramp=yes: if the way represents a ramp
rather than steps, this tag is needed
• handrail=yes: is there a handrail?
Tags in OSM
• There are numerous tags available –
check the links for a description of what
different keys and values mean
• To store accessibility information, we can
use some of the available tags; eg.
Accessibility-related OSM tags
• What about accessibility attributes for
which keys are not already available in
• Use description=“” tag, eg.
decription=manoeuvring space available
• In any case, adding tags in OSM is
welcome but optional: all accessibility
attributes should be entered in description
sheets (slide 6)!