Google Maps API V3: Zoom to State with Most Markers
Question
I have been given a requirement to set the center and zoom to the state level on the state in which I have laid the most markers on a Google Map. All the data I am working with is a collection of points (latitude/longitude).
I realize that I can make a geolocation call ( http://code.google.com/apis/maps/documentation/geocoding/index.html#GeocodingRequests - See: Reverse Geocoding) for each point and then count the states to determine which I should show but, since there will be hundreds to thousands of points per map, this is not practical.
Is there anything else I can do achieve this? Is there anything possible that would be similar (ex/ center of high concentration of markers)?
2 answers
solution1
1 2011-12-13 20:56:10
Here is an idea. Refer to this SO Question . The first answer has a link to an XML file with the polygon coordinates for all the state boundaries. You could also simplify the polygons so there are not so many vertices.
When a marker is added to the map you can check to see if it exists in one of the 50 point arrays using an algorithm like this :
UPDATE: the original function I posted was not in javascript. Here is a Javascript one and a fiddle of it working :
/*
* state == array of Google LatLng objects.
* lat == latitude to test
* lng == longitude to test
*/
function pointInPolygon(state, lat, lng) {
var polyCount = state.length;
var oddNodes = false;
var j = 0;
for (var i = 0; i < polyCount; i++) {
j++;
if (j == polyCount) {
j = 0;
}
latitudeBoundry = state[i].lat();
longitudeBoundry = state[i].lng();
latitudeBoundry2 = state[j].lat();
longitudeBoundry2 = state[j].lng();
if ((latitudeBoundry > lat && latitudeBoundry <= lat
|| latitudeBoundry2 > lat && latitudeBoundry <= lat)) {
if (longitudeBoundry + (lat - latitudeBoundry)
/ (latitudeBoundry2 - latitudeBoundry)
* (longitudeBoundry2 - longitudeBoundry) > lng) {
oddNodes = !oddNodes
}
}
}
return oddNodes;
}
If it exists increment a counter.
Once you have found the state with the most markers you can set the zoom by creating a bounds object.
//the polyArray is the array of points for the target state.
var bounds = new google.maps.LatLngBounds();
for ( var i = 0; i < polyArray.length; i++ )
{
bounds.extend( polyArray[ i ] );
}
//set the map viewport
map.fitBounds(bounds)
I have no idea about how this will pan out performance wise, but it should be much faster than reverse geocoding.
solution2
1 2011-12-14 01:42:06
Here is a sample page that implements the grid method I mentioned earlier. It's similar in concept to Bryans, but, because it just is a simple division to determine which sector in the grid, it may be a little faster on large data sets (but you do lose the state specificity):
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Auto Center</title>
<script type="text/javascript" src="http://maps.googleapis.com/maps/api/js?sensor=false"></script>
<style>
#wrap {width:960px;margin-right:auto;margin-left:auto;position:relative;}
#map_canvas {width:100%;height:700px;}
table,td {border-collapse:collapse;border:thin #000 solid;}
</style>
</head>
<body>
<div id="wrap">
<div id="map_canvas"></div>
<div id="tabular"></div>
<script type="text/javascript">
function randomFromTo(from, to){
return Math.floor(Math.random() * (to - from + 1) + from);
}
var map;
var placesToFilter=Array();
var myOptions = {zoom: 6,mapTypeControl: false,mapTypeId: google.maps.MapTypeId.ROADMAP};
//---Creating random data
for(i=0;i<500;i++){
var a=new Object();
a.lat=randomFromTo(2600,4900)/100;
a.lng=-randomFromTo(6600,12500)/100;
placesToFilter.push(a);
}
//---Get max and min latitude
var maxLat=placesToFilter[0].lat*1;
var minLat=placesToFilter[0].lat*1;
for (i=1;i<placesToFilter.length;i++) {
if (placesToFilter[i].lat*1>maxLat) {maxLat=placesToFilter[i].lat*1;}
if (placesToFilter[i].lat*1<minLat) {minLat=placesToFilter[i].lat*1;}
}
//---Get max and min longitude
var maxLng=placesToFilter[0].lng*1;
var minLng=placesToFilter[0].lng*1;
for (i=1;i<placesToFilter.length;i++) {
if (placesToFilter[i].lng*1>maxLng) {maxLng=placesToFilter[i].lng*1;}
if (placesToFilter[i].lng*1<minLng) {minLng=placesToFilter[i].lng*1;}
}
var s=8;//--------------------How many rows/columns the area gets gridded into
var latDelta=maxLat-minLat;
var lngDelta=maxLng-minLng;
var latStep=latDelta/s;
var lngStep=lngDelta/s;
var latBands=Array();
for(i=1;i<=s;i++){latBands.push(i*latStep);}
var lngBands=Array();
for(i=1;i<=s;i++){lngBands.push(i*lngStep);}
//---Keeping score in these arrays
var gridCount=new Array();
for(var x=0;x<s;x++){
for(var y=0;y<s;y++){
var cell=[x,y];
gridCount.push(cell);
}
}
for(var lt=0;lt<s;lt++){
for(var lg=0;lg<s;lg++){
gridCount[lt][lg]=0;
}
}
map = new google.maps.Map(document.getElementById('map_canvas'),myOptions);
for(p=0;p<placesToFilter.length;p++){
//---Keeping track of which grid sector
var whichLat=Math.floor((placesToFilter[p].lat-minLat)/latStep);
var whichLng=Math.floor((placesToFilter[p].lng-minLng)/lngStep);
gridCount[whichLat][whichLng]++;
//---And placing the marker
var point=new google.maps.LatLng(placesToFilter[p].lat,placesToFilter[p].lng);
var marker = new google.maps.Marker({position: point,map: map});
}
//---Figuring out which cell 'won'
var checking=gridCount[0][0];
var rightLat;
var rightLng;
for(lt=0;lt<s;lt++){
for(lg=0;lg<s;lg++){
if(gridCount[lt][lg]>checking){
checking=gridCount[lt][lg];
rightLat=lt;
rightLng=lg;
}
}
}
//convert grid sector to lat/lng (center of sector)
var winningLat=maxLat-(rightLat*latStep)-(latStep/2);
var winningLng=minLng+(rightLng*lngStep)+(lngStep/2);
var newCenter=new google.maps.LatLng(winningLat,winningLng);
map.setCenter(newCenter);
showTable=true; //--------------this will display the table of data so you can see how many markers are in each sector
if(showTable){
var table='<table>';
for(row=0;row<s;row++){
table+='<tr>';
for(td=0;td<s;td++){
table+='<td>'+gridCount[row][td]+'</td>';
}
table+='</tr>';
}
table+='</table>';
document.getElementById('tabular').innerHTML=table;
}
</script>
</div>
</body>
</html>
The technical post webpages of this site follow the CC BY-SA 4.0 protocol. If you need to reprint, please indicate the site URL or the original address.Any question please contact:yoyou2525@163.com.