topic How to convert map scale to web map zoom level in ArcGIS Online Questions

How to convert map scale to web map zoom level

DavidAglietti — Fri, 05 Dec 2014 07:56:33 GMT

Hello,

I would like to determine how to a convert specific map scale to the closest zoom scale used by the major web mapping players. For example, I want to open a web map to whatever predefined scale is closest to 1:100,000 or whatever cached scale is closest. How do I calculate the zoom level knowing that this is the established breakdown, and that the answer that I'm looking for is 10?:

20 : 1128.497220 19 : 2256.994440 18 : 4513.988880 17 : 9027.977761 16 : 18055.955520 15 : 36111.911040 14 : 72223.822090 13 : 144447.644200 12 : 288895.288400 11 : 577790.576700 10 : 1155581.153000 9 : 2311162.307000 8 : 4622324.614000 7 : 9244649.227000 6 : 18489298.450000 5 : 36978596.910000 4 : 73957193.820000 3 : 147914387.600000 2 : 295828775.300000 1 : 591657550.500000

There must be an elegant way to do this, but my math.foo is weak after all these years of being out of school and withering away in meetings.

Thanks for your help,

Ryan

Re: How to convert map scale to web map zoom level

DavidAglietti — Fri, 05 Dec 2014 08:55:51 GMT

Ah ha! I found the key to the answer by applying some google-foo, wine, and much confused panic recall of algebra i thought i would never use. I'll post the answer so I become rich and famous, as all GIS old guys should do.

Here is where I found the logic for the cached map scale logic:

What ratio scales do Google Maps zoom levels correspond to? - Geographic Information Systems Stack Exchange

and this response led to the answer:

http://gis.stackexchange.com/a/81390‌

Many thanks to these folks as this would have been impossible for me to figure out on my own.

For posterity in javascript form:

alert(Math.round(Math.log(591657550.500000 /(<your map scale>/2))/Math.log(2)));

This should return an integer value that corresponds to the zoom level (rounded) once you supply the scale.

Try it in JsFiddle:

Edit fiddle - JSFiddle

Hope this helps someone else, I was lost on this one for a time and considered knitting as an alternative career.

D. Ryan

Re: How to convert map scale to web map zoom level

DerrickWestoby1 — Wed, 24 Apr 2019 15:23:17 GMT

This (5 year old) post helped me a lot. Thanks David!

calculate

convert_zoom1

Testing

log(591657550.500000 div (${map_scale} div 2))

calculate

convert_zoom2

testing

log(2)

calculate

convert_zoom3

testing

${convert_zoom1} div ${convert_zoom2}

calculate

web_zoom

testing

round(${convert_zoom3}, 0)