Hi, Inspired by seeing the estimate in the Microgrant application of 5.5 million buildings on the island of Ireland, I did some number crunching.
I downloaded the populations of Kilkenny townlands (1,500+) from the CSO and analysed the population against the number of buildings per civil parish (100+) for County Kilkenny. This is assuming Kilkenny has all or nearly all buildings mapped. Based on my inspections, this is largely true. The CSO data is somewhat distorted for the Kilkenny city area (100+ townlands), due to the way the CSO have arranged the townlands and civil parishes. I could look at this in more detail, but there would be a few hours of effort (unless someone has a simple way of calculating number of buildings per area, for a large number of areas). I calculated the 'number of buildings per civil parish' using the Overpass Turbo query [building=* in "civilparishname, Kilkenny"]. Overpass Turbo gives a summary of the data in the bottom right corner of the screen, e.g. Loaded – nodes: 4261, ways: 867, relations: 2 Displayed – pois: 0, lines: 0, polygons: 866 I took the number of polygons to mean the number of buildings (this might not be perfect - I don't know how those numbers add up). Additionally, some polygons, e.g. building=terrace represent several buildings, while in other cases buildings may have been crudely split or joined-up. Depending on the civil parish, we're looking at 0.32-2.29 polygons per capita (0.44-3.15 people per building). Rural areas ten to have more polygons per capita, especially due to farm outbuildings, while urban areas have fewer polygons per capita, due to apartments buildings and semi-detached buildings (e.g. two square houses joined together might have only six nodes). I also calculated 4.40-5.83 nodes per polygon. This means some civil parishes have predominantly rectangular polygons / buildings, whereas others have many L-shaped or other-shaped polygons / buildings. As I wasn't able to immediately get some 'number of buildings per civil parish' numbers (Overpass Turbo had problems returning them, possibly due to duplicate names and variations in name spellings), I had to calculate them from their component townlands, using the Overpass Turbo query [building=* in "townlandname, civilparishname, Kilkenny"]. Depending on the townland, we're looking at 0.23-8.00 polygons per capita (0.13-4.37 people per building) and 3.91-6.45 nodes per polygon (i.e. some townlands have large numbers of semi-detached or terraced buildings, whereas others have a high number of complicated-shape polygons / buildings or buildings with too many mapped nodes). It is usual to see more extreme spreads when looking at smaller areas. I'm coming up with about 5.4 million (close enough!) buildings for the whole island, assuming the pattern is the same everywhere. However, as shown by analysing the smaller areas, there is variation and the 'final' number will vary from that. Of course, given that OSM is an ongoing project, there will never be a final number. Colm VictorIE _______________________________________________ Talk-ie mailing list Talk-ie@openstreetmap.org https://lists.openstreetmap.org/listinfo/talk-ie
