|Used to describe many different sorts of buildings, including houses, factories and ruined buildings.|
A single building outline can be created for each building complex or 'block', which may relate to a single detached property, or to a row of individual terraced houses or to some more complex arrangement of properties. It is however better to create a series of linked outlines which share some nodes at the boundary to identify each distinct part of the property.
In addition outlines can either be simplified shapes or very outlines which conform very accurately to the shape of the building. It is not uncommon for buildings to initially be described as simple group outlines later be improved with more detailed outlines and to be split into individual properties.
Buildings can simply be building=yes or use a value that describes the building typology, for example building=house, building=hut, building=garage, building=school. See building=* for a more complete list of options and have a look at what is actually used.
The address of the building can also be added. This can either be attached to the building outline, or more usefully to the appropriate main entrance which should have a node tagged with entrance=yes or entrance=*.
For larger public building with many entrances for different purposes and for us by different people the building entrance can also be tagged with a access=*. A building entrance can be connected to a description of the footpath access to the entrance by highway=footway and highway=steps etc. Where appropriate multiple entrances can have appropriate postal addresses.
Many mappers are using the key building=* to describe moveable objects and buildings for example building=static_caravan and building=houseboat. Differing from the ideal of mapping the outline of a building on the ground, many objects with building=* include parts of buildings (for example constructed on piers) which are only covering areas. building=roof even describes a building which has, except its piers, no outline on the ground.
How to map
When tracing from aerial imagery try to estimate the place where the building position on the ground which may be offset from the roof-line as shown by the imagery on the far side given that images are normally taken from an angle.
If the building has an interior courtyard the use a Multipolygon relation to ensure that the courtyard is not rendered as part of the building.
- As a lot of buildings are rectangular, you can draw a rough rectangle, and then orthogonalize it in JOSM with the hotkey 'Q'. Pressing Q on a selection sets all the angles in the selection to be 90°. Be sure you're using a projection like Mercator, otherwise if you use something like WGS84, then objects will be distorted when rendered. (Please be aware that not all buildings are orthogonal and sometimes it is better to keep an odd looking polygon instead of making a curved shape rectangular.)
- JOSM/Plugins/BuildingsTools makes mapping of buildings a lot more convenient (hotkey 'W'). This works best for buildings with four nodes.
- JOSM/Plugins/Terracer is for quickly mapping a row of terraced houses.
In Potlatch, you can add several buildings quickly especially in residential areas by tracing the building with one hand with the mouse and then with the other hand pressing the 'R' key to add the properties of the previously selected building. Add the source, building tag and whatever other tag you want on the first building then copy it to the other buildings.
Some ways to get the outline of the building
- Aerial photographs (e.g. Bing). There are also some tips and tricks for roof modelling.
- Observations from street level, drawing a sketch, or even taking measurements
- Walking around the edge of the building taking a GPS trace. Good enough for big buildings (e.g. a stadium) but being close to walls is bad for GPS accuracy.
- French Cadastre
- shop=* to indicate that the building is used as a specific shop
- amenity=* to describe what the building is used for, for example: school, theatre, bank, ...
- entrance=* to mark the entrances to the building
- architect=* to indicate the architect of a building
- building:condition=* for the condition of the building
- ruins=* - for ruins of buildings
- abandoned=* - for a building which has been abandoned by its owner and is no longer maintained
- start_date=* - the year of construction
Use the Simple 3D Buildings that is already implemented in some tools and offers backwards compability with previous approaches.
- Proposed features/Building - original proposal, which mentions various other ideas
- Proposed features/Building attributes - attributes proposal, cancelled
- Relations/Proposed/Buildings - (to group buildings and other related things together)