Population Density
The command Population Density on the Grid menu enables to assign residents to buildings (see Building). This feature is - for example - useful when the number of residents per building is not available, but house-specific evaluations are required. Besides, an corresponding population density (in inhabitants/km²) can be assigned the existing areas of designated use (see Area of Designated Land Use). The operation affects all active buildings.
On the dialog Calculate Population Density a formula based on the following variables of the buildings can be entered
- F Area (m²)
- U Perimeter Length (m),
- H Height (m) and
- L Longest Side (m)
to calculate the number of inhabitants per building.
Dialog options
Calc Residents per Building
Enter a formula by using the variables F, U, H and L to calculate the number of residents. By default, the following formula is used:
f/40 * h/3
This expression means that on average 40 m² floor area is allocated per person and that the storey height on average is 3 m.
After clicking OK, all buildings marked as „Residential Building“ (see Building), the number of residents is calculated using the entered formula and written to the buildings (see dialog Building and menu Tables|Obstacles| Building, column „Residents“).
Example
A building has a floor area of 244.95 m² and a height of 12 m. The number of residents results from:
244.95/40 * 12/3 = 24.494951 residents
In the dialog Building the integer value (7) is displayed:
Number of residents displayed as integer value
Internally, however, the calculated decimal value is still used. This can be seen by writing the value of attribute EINW (=number of residents) into a string variable of the building (see Modify Attribute, Example 6: Writing an attribute to a string variable in the manual "Introduction to CadnaA"):
Internal number of residents represented by a decimal number
Note
This difference in the representation of figures may lead to differences when summing up residents when, on one hand, integers are summed up and, on the other hand, are compared with results from object scanning (see Object-Scan), using the internal representation of the number of residents being a decimal value.
Calculate Population Density in Areas of Land Use
For the calculation of the inhabitants/km² of areas of designated use requires first, that there are such areas available (see Area of Designated Land Use).
Attribute "inhabitants/km²" usage areas
Furthermore, buildings within those areas of designated use must be available, the residents of which serving as the data basis for the calculation.
Note
In order to calculate the residents of buildings, however, no areas of designated use must be present.
After clicking OK, all areas of land use and, further, all buildings are scanned evaluating the residents, either based on the entered number (with option „Calc Residents per Building“ inactive) or by using the entered formula (with this option active). In conjunction with the area of each areas of land use the population density (in inhabitants/km²) results.
Example
A single area of land use, area 5000 m² = 0.005 km², with a building having 6.666667 residents results in 6.666667/0.005 = 1333.33 inhabitants/km².
In case multiple areas of land use overlap, the evaluation occurs just for the most recently entered area (top layer).
Normalize to Actual Number of Inhabitants
With this option active, the number of residents of all active buildings is normalized using the specified actual number of inhabitants so that the total number of residents in the area (project) equals the number specified. Enter the actual „Number of Inhabitants in Entire Area“. The new number of residents is written to each building.
Example
All active buildings in the entire area (project) may have a total number of residents SUM_RESID (sum of all attributes EINW). The new number of residents RESID_NEW results from the „Number of Inhabitants in Entire Area“ INHAB_AREA and the residents per building EINW from:
RESID_NEU = INHAB_AREA / SUM_RESID * EINW