Editing Space syntax (section)

===Choice===
The choice measure is easiest to understand as a 'water-flow' in the street network. Imagine that each street segment is given an initial load of one unit of water, which then starts pouring from the starting street segment to all segments that successively connect to it. Each time an intersection appears, the remaining value of flow is divided equally among the splitting streets, until all the other street segments in the graph are reached. For instance, at the first intersection with a single other street, the initial value of one is split into two remaining values of one half, and allocated to the two intersecting street segments. Moving further down, the remaining one half value is again split among the intersecting streets and so on. When the same procedure has been conducted using each segment as a starting point for the initial value of one, a graph of final values appears. The streets with the highest total values of accumulated flow are said to have the highest choice values.

Like integration, choice analysis can be restricted to limited local radii, for instance 400m, 800m, 1600m. Interpreting Choice analysis is trickier than integration. Space syntax argues that these values often predict the car traffic flow of streets, but, strictly speaking, choice analysis can also be thought to represent the number of intersections that need to be crossed to reach a street. However, since flow values are divided (not subtracted) at each intersection, the output shows an exponential distribution. It is considered best to take a log of base two of the final values in order to get a more accurate picture.