Using Nokia/Yelp Map API for finding POIs in an area

Question

The first place to look would be the developer documentation site of the relevant API. For the Nokia APIs you would be looking at the JavaScript documentation or the RESTful Places API, for Yelp try the links under http://www.yelp.com/developers/ (disclaimer - I don't personally use Yelp)

There are numerous examples using the Nokia Place apis held within the API explorer to play with and see the results on screen.

Here are a couple of useful examples to get you started

Both the Nokia Places API and the Yelp API are local search APIs - in other words they always answer the question "Where can I find an X near Y?", so finding total number of POIs in their database is not a realistic task (since many POIs will be considered irrelevant to a search location, what you could do is find the density of POIs within a specific location.

The code below will initially show bookshops in central Berlin, but if you change the Focus of the map it will find bookshops in other towns as well. You need to obtain your own free app id and token to get it to work.

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<!-- 
    Example from Nokia Maps API Playground, for more information visit http://api.maps.nokia.com
 -->
<html xmlns="http://www.w3.org/1999/xhtml">
    <head>
        <meta http-equiv="X-UA-Compatible" content="IE=7; IE=EmulateIE9"/>
        <meta http-equiv="content-type" content="text/html; charset=UTF-8"/>
        <title>Nokia Maps API Example: Search by category</title>
        <meta name="description" content="Search by category"/>
        <meta name="keywords" content="search, services, places, category"/>
        <!-- For scaling content for mobile devices, setting the viewport to the width of the device-->
        <meta name=viewport content="width=device-width, height=device-height, initial-scale=1.0, maximum-scale=1.0, user-scalable=no"/>
        <!-- By default we add ?with=all to load every package available, it's better to change this parameter to your use case. Options ?with=maps|positioning|places|placesdata|directions|datarendering|all -->
        <script type="text/javascript" charset="UTF-8" src="http://api.maps.nokia.com/2.2.3/jsl.js?with=all"></script>
        <!-- JavaScript for example container (NoteContainer & Logger)  -->
        <style type="text/css">
            html {
                overflow:hidden;
            }

            body {
                margin: 0;
                padding: 0;
                overflow: hidden;
                width: 100%;
                height: 100%;
                position: absolute;
            }

            #mapContainer {
                width: 80%;
                height: 80%;
                left: 0;
                top: 0;
                position: absolute;
            }
            #progress {
                width: 80%;
                height: 10%;
                left: 0;
                top: 80%;
                position: absolute;
            }
            #buttons {
                width: 80%;
                height: 10%;
                left: 0;
                top: 90%;
                position: absolute;
            }
        </style>
    </head>
    <body>
        <div id="mapContainer"></div>
        <div id="progress"></div>
        <div id="buttons">
         <a onClick="searchByCategory( map.center, 'bookshop' );return false;" href="#">Find Bookshops</a> 
        </div>
        <script type="text/javascript" id="exampleJsSource">
/*  Set authentication token and appid 
*   WARNING: this is a demo-only key
*   please register on http://api.developer.nokia.com/ 
*   and obtain your own developer's API key 
*/
nokia.Settings.set("appId", "YOUR APP_ID"); 
nokia.Settings.set("authenticationToken", "YOUR TOKEN");


// Get the DOM node to which we will append the map
var mapContainer = document.getElementById("mapContainer");
// Create a map inside the map container DOM node
var map = new nokia.maps.map.Display(mapContainer, {
    // Initial center and zoom level of the map
    center: [52.51, 13.4],
    zoomLevel: 10,
    components: [       
        new nokia.maps.map.component.Behavior()
    ]
});

var searchManager = nokia.places.search.manager,
    resultSet;


var searchCat;  
var maxDistance = 0;

// Function for receiving search results from places search and process them
var processResults = function (data, requestStatus, requestId) {
    var i, len, locations, marker;



    if (requestStatus == "OK") {
        // The function findPlaces() and reverseGeoCode() of  return results in slightly different formats
        locations = data.results ? data.results.items : [data.location];
        // We check that at least one location has been found
        if (locations.length > 0) {
            // Remove results from previous search from the map
            if (resultSet) map.objects.remove(resultSet);
            // Convert all found locations into a set of markers
            resultSet = new nokia.maps.map.Container();
            for (i = 0, len = locations.length; i < len; i++) {
                marker = new nokia.maps.map.StandardMarker(locations[i].position, { text: i+1 });
                resultSet.objects.add(marker);
                if (locations[i].distance > maxDistance){
                    maxDistance = locations[i].distance;
                }
            }
            // Next we add the marker(s) to the map's object collection so they will be rendered onto the map
            map.objects.add(resultSet);
            // We zoom the map to a view that encapsulates all the markers into map's viewport
            map.zoomTo(resultSet.getBoundingBox(), false);


            progressUiElt.innerHTML = locations.length  + " places found in the '" + searchCat + "' category within " + maxDistance + "m of "+ data.search.location.address.city ;
        } else { 
            alert("Your search produced no results!");
        }
    } else {
        alert("The search request failed");
    }
};



// Binding of DOM elements to several variables so we can install event handlers.
var progressUiElt = document.getElementById("progress");


searchByCategory = function(searchCenter   , category){
// Make a place search request
searchCat = category;
progressUiElt.innerHTML = "Looking for places in the '" + category + "' category...'";
searchManager.findPlacesByCategory({
    category: category,
    onComplete: processResults,
    searchCenter: searchCenter,
    limit: 100,
});
}
// Search for Bookshops in Berlin
searchByCategory( new nokia.maps.geo.Coordinate(52.51, 13.4), "bookshop" );

        </script>
    </body>
</html>

So you can see that there are over 100 bookshops in Berlin, but only 37 in Potsdam for example.