Am I Near Public Art? How about Crime?

26 Feb

When you are new to a city, it is hard to walk around and carry a map of all the sites. Wouldn’t it be nice if your phone could alert you when you were near something of interest? In this post, I will show you how to create an alert system.

The Application

The application will build off of our earlier post using Albuquerque Crime Data. In that application, the user clicked the map and was presented with all crimes in the last 180 days within a half mile of the click.

This application will use the same logic but replace the click with the users location.

Building the Application

We will start with a Leaflet.js Mobile map. Place the following HTML in the head of your document.

<meta name=”viewport” content=”width=device-width, initial-scale=1.0, maximum-scale=1.0, user-scalable=no” />

body {
padding: 0;
margin: 0;
html, body, #map {
height: 100%;

This will make the map look nice on mobile – and desktop as well. Then create the map.

var map =‘map’);


map.locate({setView: true, maxZoom: 16,enableHighAccuracy:true,watch:true});

With mobile maps, we do not pass the setView to the map, we add that parameter to the locate() function. Now we need two functions: one for found and one for not found.

map.on(‘locationfound’, gotcha);

function gotcha(e){ALL OUR CODE GOES HERE}

map.on(‘locationerror’, onLocationError);

function onLocationError(e) {

When our location is found, we want to setup the buffer and prep for calling the Albuquerque Data for Public Art or Incidents.

b=a.toGeoJSON();, 20).addTo(map);
buffered = turf.buffer(b,.05,”miles”);
var result = turf.featurecollection(buffered.features.concat(b));

We create a marker, convert it to GeoJSON to use with Turf.js, then buffer and get the rings to use in the query.

Now we can make our standard AJAX call to an ESRI REST Endpoint. I have commented out the URL for Public Art and the marker. You can uncomment them and comment out the incident url and marker to switch the application.

var params=”f=json&outSR=4326&outFields=*&geometryType=esriGeometryPolygon&spatialRel=esriSpatialRelIntersects&inSR=4326&geometry=”+g;

//var url = “;;
var url = “;;
http=new XMLHttpRequest();“POST”, url, true);
http.setRequestHeader(“Content-type”, “application/x-www-form-urlencoded”);
http.onreadystatechange = function() {//Call a function when the state changes.
if(http.readyState == 4 && http.status == 200) {
var result= JSON.parse(http.responseText);


Now we get back all the incidents, or art, within 300 feet (.05 miles) of our location. We need to take the results and add them to the map and notify the user they are near something of interest.



As we move, the service is queried again, constantly watching us and letting us know when we are near something of interest. The vibration pattern is 100ms for each feature we are near and pause for 100ms between each feature. If we are near a lot of features -say crime incidents – our phone will vibrate many times. Possibly signaling a dangerous part of town. If we are using public art, we know we are near a particularly artistic part of the city and maybe we should explore more.

To use the same map for multiple features, you could switch up the vibration patterns, say short fast vibrations for art and longer for crime. Maybe vibrate once for crime but the duration is a function of the number of incidents – 10 incidents results in a 10 second vibration.

Just an idea on how to use open data to alert new comers to the features of the city that they may not be aware of.


2 Responses to “Am I Near Public Art? How about Crime?”

  1. Anon February 26, 2015 at 6:28 pm #

    If you are so lacking in awareness of your own surroundings that you can neither recognize danger nor art, a mobile device will not be able to save you. The thieves will make off with your loot, and no one will feel pity.

    • paulcrickard February 26, 2015 at 6:31 pm #

      The point is not to save you, but if you are a tourist, there may be things you are not aware of. 300 feet in a city is a long way. You can’t know what’s around the corner. Those two features were used because they were public.

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