Set your parcel and street dimensions, then click Compute to see the optimal block layout.
The gravity accessibility curve will appear here after computation.
How It Works
This calculator determines the urban block size that maximizes pedestrian accessibility to all surrounding parcels. For a given set of parcel and street dimensions, it simulates urban grids with varying numbers of plots per block frontage (PPF) and computes the mean Hansen gravity accessibility from a central block.
The Gravity Model
Pedestrian accessibility for each parcel is computed as:
where d[i,j] is the shortest network distance between parcel entrances, β controls distance decay (willingness to walk), and r is the maximum search radius.
The Nonlinear Relationship
While shorter blocks create more intersections and route choices, they also introduce more street crossings (each adding distance cost) and reduce the number of parcels reachable within a fixed walking radius. Conversely, longer blocks reduce crossings but impose detours. The result is a parabolic relationship: both excessively short and excessively long blocks reduce accessibility, with an intermediate "optimal" block size maximizing it.
What Affects the Optimal Block Size?
Wider streets shift the optimal block length upward, as each street crossing becomes costlier, favoring fewer but longer blocks. Greater willingness to walk (lower beta) also favors longer blocks, since pedestrians who walk further can tolerate the detours that longer blocks impose. Parcel dimensions affect how many destinations fit within a walking radius at each block size.
Parameters
Plot Frontage: Width of each parcel along the street (meters).
Plot Depth: Depth of each parcel perpendicular to the street (meters).
Street Width X: Width of horizontal streets (meters).
Street Width Y: Width of vertical streets (meters).
Beta: Distance decay parameter. Lower values indicate greater willingness to walk. Typical range: 0.001-0.01 for distances in meters.
Search Radius: Maximum walking distance considered (meters). Typically 1000-1500m for utilitarian walking trips.