Algorithm 2: Build an Area Summary

Input: $AG$: a tuple ($key$, L), where $key$ is a pair (area, time period) and L is a list of taxi information  Output: $ASP$: a pair (spatio-temporal hash-key $key$, an area summary $AS$) 1 Initialize $AS$ as Area Summary;  // calculate area summary value 2 $A{S}_{key}$ ← $A{G}_{key}$; 3 $A{S}_{key}.{\mu }_f$ is calculated from each group of $A{G}_{key,L}$; // Equation (2) 4 $A{S}_{key}.List$ is computed from each group of $A{G}_{key,L}$; // Equation (3) 5 $A{S}_{key}.pd$ is calculated from each group of $A{G}_{key,L}$; // Equation (4) 6 $ASP$ ← pair($A{G}_{key}$,$AS$); 7 return $ASP$;