LaudonTech's GIS Blog

I’ve never really liked using the scale values on a computer screen. The scale would depend on the dot size (DPI) of your screen. Imagine plugging your computer to a projecter. Then those values are really wrong.
Also remember that the scale continuously changes in the north/south direction because of the Mercator projection.

These values are dependent on the latitude at which you measure them and and assumed physical size of a pixel on your monitor. Numeric scale Google maps = Mass confusion. The dynamic scale bar Google uses is far the best way to communicate ground size.

I actually did a visual comparison of the Google Map on one monitor and an ESRI GIS map of the same area on the other monitor and recorded the scales. I understand they are not accurate, however, close enough for my purposes, er, at least around the 49th parallel.

Let me guess, you want to use that information in order to generate a tiling scheme for ArcGIS Server cache files (GenerateMapServerCacheTilingScheme)?! Have you been successful?

Not a bad idea…but I was actually just figuring out what reference scales to symbolize the data to for creating my own custom Google Maps tiles.

I would like to set my scale base on 1 mile view, 2 mile view, 3 mile views, will google let you create your own zoom level for example I want to create a zoom at 1:16,000

How about the width and height of the tiles per zoom level? And how do you determine the amount of rows and columns per zoom level? Anyone know?

I’ve made some calculations, and I do not reach the same scale values.
I use the tilling scheme provided by google to calculate envelope’s in each zoom level.
(Remember that Google Maps use Mercator meters)

Here are my results:

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

PS. you don’t have to know these scale values to create a tiling scheme for ArcGIS Server

[...] de 2x a 17x, a la verdad eso no se puede asociar a una escala fácilmente, ya algunos han hecho sus aproximaciones, llegando a buenos niveles de [...]

[...] de 2x a 17x, a la verdad eso no se puede asociar a una escala fácilmente, ya algunos han hecho sus aproximaciones, llegando a buenos niveles de [...]

As Morton pointed out, these numbers are pretty much useless. What is needed is “meters per pixel” at every zoom level. That’s what the dynamic scale bar is showing.

Take a look at the conversion table from ESRI:

http://blogs.esri.com/Support/blogs/mappingcenter/archive/2009/03/19/How-can-you-tell-what-map-scales-are-shown-for-online-maps_3F00_.aspx

you would never be able to compare two different cities in size , for example paris and nyc. because the scale is different for each area . it means that 2 miles looks different in paris than in nyc , this is a bug , hopefully google will discover this problem and fix it. try to put the scale at 2 miles in nyc and then for paris , you will see that you won’t be able to get the same distance for 2 miles in each city , in paris for example 2 miles will show up as 2miles = 1 inch , but when you scroll to nyc , yes that is a long scroll , the scale will suddenly change to 2 miles = 1,5 inch , and there is no way to escape this bug . too bad , now it is hard to put 2 cities next to eachother from different maps to see the size of a town compare to another city.

This is what i use:
1128.497176
2256.994353
4513.988705
9027.977411
18055.954822
36111.909643
72223.819286
144447.638572
288895.277144
577790.554289
1155581.108577
2311162.217155
4622324.434309
9244648.868618
18489297.737236
36978595.474472
73957190.948944
147914381.897889
295828763.795777
591657527.591555

mapping to MapInfo’s Zoom window width using stare and compare in the Louisville, Ky area:

multiply width by 2 on up
16 = 1.5 mi
17 = .75
divide width by 2 on down

I want to start blogging too, what do you think, which blog platform is good for noob?

I just wanted to say your site is one of the nicely laid out, most inspirational I have come across in quite a while. Thx!

@zroq: The difference in scale is not a bug. Google Maps uses a map projection similar to the Mercator projection. This means that the closer you get to the poles, the larger everything becomes. There’s no helping it if you have to project a sphere onto a plane. To test this, simply zoom out a bit and drag north or south, and you will see the scale change dynamically.