Monday, July 13, 2015

A Safe Walk in LA

The Los Angeles Times has mapped over half a million pedestrian accidents in L.A. County in order to visualize the county's most dangerous intersections. Walking in LA uses data from the California Highway Patrol to provide a heatmap of the most dangerous intersections for pedestrians.

The heatmap highlights more than 800 intersections which have a higher rate of pedestrian injury or death than the county averages. The 817 dangerous intersections are also available to be viewed in list form.

Map developers will be interested in this How We Did It article on how the map was created. The article explains how the data was collected, processed and mapped. The heatmap data was added to the map tiles using TileMill, which is an economic way to visualize a large amount of data on an interactive map.

The map uses the Leaflet.label plugin to add labels to some of the most dangerous intersections. The labels are then connected to the highlighted locations using a custom pointer, created by writing a small extension to L.Path (the JavaScript is provided in the article if you want to copy this idea).

The LA Times article points out that many of the most dangerous intersections are in some of the densest neighborhoods. This doesn't mean that the map should be normalized by the amount of pedestrian traffic. If you wanted to reduce the number of pedestrian accidents as much as possible it would make sense to try and increase the safety at the intersections which are responsible for the most accidents whether or not they have the most foot traffic.

However it is interesting to compare the LA Times map of the most dangerous intersections with Eric Fischer's Daily Pedestrian Extrapolation map. This map shows intersection pedestrian counts (extrapolated to daily totals). The two maps do seem to show that many of the most dangerous intersections in LA are the intersections with a high foot traffic, particularly in the Downtown area.

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