The urbansim_constants table

Constants needed for calculations made by the various models.

A single row with one column per constant.

Column Name	Data Type	Description
cell_size	float	Width and height of each grid cell in units
units	varchar	Units of measurement, eg. ``meters'' or ``feet''
walking_distance_circle_radius	float	Walking distance in meters, e.g., 600 m, R in the descriptions
young_age	integer	Max age for a person to be considered young
property_value_to_annual_cost_ratio	float	Ratio of the total property value to an annual rent for that property
low_income_fraction	float	Fraction of the total number of households considered to have low incomes, e.g., 0.1
mid_income_fraction	float	Fraction of the total number of households considered to have mid-level incomes, e.g., 0.5
near_arterial_threshold	float	Line distance from the centroid of a cell to an arterial for it to be considered nearby, e.g., 300. NearArterialThreshold in description.
near_highway_threshold	float	Line distance from the centroid to a highway for it to be considered nearby, e.g., 300. NearHighwayThreshold in description.
percent_coverage_threshold	integer	The threshold above which a grid cell's percent_*, e.g. percent_wetland, must be to be considered ``covered'' for that attribute. So, if percent_coverage_threshhold is 50 percent and percent_wetland is 60 percent, the grid cell would be considered ``covered'' by wetland.
recent_years	integer	Maximum number of years to look back when considering recent transitions. For example, if recent_years = 3, then the value commercial_sqft_recently_added in the gridcells table would refer to the number of square feet of commercial space built in the last 3 years.

• cell_size must be greater than zero
• units must be one of the following: meters, feet, miles, kilometers.
• walking_distance_circle_radius must be greater than zero and <= absolute_max_distance
• walking_distance_circle_radius must result in less than 250 grid cells within walking distance
• young_age must be greater than zero and <= absolute_max_person_age
• property_value_to_annual_cost_ratio must be greater than zero
• low_income_fraction must be between 0 and 1
• mid_income_fraction must be between 0 and 1
• mid_income_fraction + low_income_fraction must be at most 1.
• near_arterial_threshold must be greater than zero and <= absolute_max_distance
• near_highway_threshold must be greater than zero and <= absolute_max_distance
• percent_coverage_threshold must be between zero and 100. Note that this value is exclusive; for example, if the value is set to 45 and a grid cell is 45% covered by roads, the cell will not be considered to be ``covered'' by roads.
• recent_years must be > 0 and <= absolute_max_recent_years