reachable [accessible-all] agreagated areas

[gacafe]

• [ ] reachable aggregated areas from a centre, using buildings as the indicator of whether they are reachable. ie. if i can reach any building in the area, the area is considered "reachable"
• [ ] visualise this in the ui - how? its not a histogram, its like when you do reachable buildings they all get highlighted, but the areas need highlighting too somehow