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Calculating built-up area as a percentage of total surface area
I have a question regarding the calculation of built-up area as a percentage of the total surface area using TQL queries. Built-up area is in this case defined as the total area with a specific function (housing, offices, roads but also functions like grassland, etc.).
I use the following query/calculation to calculate the unbuilt area (Neighborhood 26 is the neighborhood/project area on which I want to perform the calculation):
- SELECT_LANDSIZE_WHERE_NEIGHBORHOOD_IS_26 - SELECT_LOTSIZE_WHERE_NEIGHBORHOOD_IS_26
According to the TQL page on the wiki the definitions of LANDSIZE and LOTSIZE are as follows:
- LANDSIZE: Amount of surface area. (m2)
- LOTSIZE: Amount of surface area used by a construction. (m2)
My assumption would be that LANDSIZE and LOTSIZE would be equal if the whole area is covered with constructions. However, after filling the total area with a construction (in a test run or session), I still have a slight difference between LANDSIZE and LOTSIZE: my LANDSIZE is 78501 m², and my LOTSIZE results in 76255 m² (a 2.8% difference in area).
How can this difference be explained? There is some water in this area (±1000 m²), which could explain some of the difference between the two values, but still doesn't account for the full 2.8% difference.
Thanks in advance!