jQuery function to return google map zoom level

Question

as referenced at http://laudontech.com/GISBlog/?p=28 , I know the scale in meters for google map zoom levels:

Zoom level 0 1:20088000.56607700 meters

Zoom level 1 1:10044000.28303850 meters

Zoom level 2 1:5022000.14151925 meters

Zoom level 3 1:2511000.07075963 meters

Zoom level 4 1:1255500.03537981 meters

Zoom level 5 1:627750.01768991 meters

Zoom level 6 1:313875.00884495 meters

Zoom level 7 1:156937.50442248 meters

Zoom level 8 1:78468.75221124 meters

Zoom level 9 1:39234.37610562 meters

Zoom level 10 1:19617.18805281 meters

Zoom level 11 1:9808.59402640 meters

Zoom level 12 1:4909.29701320 meters

Zoom level 13 1:2452.14850660 meters

Zoom level 14 1:1226.07425330 meters

Zoom level 15 1:613.03712665 meters

Zoom level 16 1:306.51856332 meters

Zoom level 17 1:153.25928166 meters

Zoom level 18 1:76.62964083 meters

Zoom level 19 1:38.31482042 meters

I want to use this information to create a function like so:

function getZoomLevel(meters) {
    //take input in whole meters
    //return best match for zoom level as integer
}

I've thought about doing nested if else greater/less then conditions, but isn't there a more streamlined approach?

Answer 1

Each decrease of the zoom level means doubling the meters, so you don't have to store each individual value.

You could try this:

function getZoomLevel(m){
    var z=0;
    var i=20088000;
    while(i/2>=m && z<19){
        z++;
        i=i/2;
    }
    return z;
}

it returns the next smaller zoom level as soon as meters is exceeding the current level.

or better:

function getZoomLevel(m){
    var z=Math.floor((Math.log(20088000/m))/Math.log(2));
    if (z>19) z=19;
    if (z<0) z=0;
    return z;
}

Answer 2

If you stored the zoom levels in an array, eg

var zoomLevels = [
    20088000.56607700,
    10044000.28303850,
    5022000.14151925,
    2511000.07075963
    // etc. ...
];

Then iterate for a best fit. Because it is known that the zoom level array is decreasing, the search will be O(n) .

function getZoomLevel(meters) {
    for (var idx = 0; idx < zoomLevels.length; ++idx) {
        if (zoomLevels[idx] < meters) {
            return idx;
        }
    }
    return zoomLevels.length - 1;
}