Don’t buildings have tags? Did I see a residential tag? Is it used in all cases?
> On 13 May 2020, at 13:24, Colm Moore <colmmoor...@hotmail.com> wrote: > > 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 _______________________________________________ Talk-ie mailing list Talk-ie@openstreetmap.org https://lists.openstreetmap.org/listinfo/talk-ie
