Comments on: Map Scales and Printing with Mapnik

By: Mark

Mark — Wed, 02 Jun 2010 18:48:01 +0000

In the notes section of this tutorial you mention to get the actual bounding box of the image you need to call the envelope() function on the map object. Using the mapnik python script generate_image.py could you explain how you call the envelope() function on the map object once you’ve used zoom-to-box(). Thank you,

Mark

By: BalRam

BalRam — Tue, 29 Sep 2009 04:31:42 +0000

Hi Andrew,

I will try it out.

Thanks for your help !!!

BalRam

By: Andy

Andy — Fri, 25 Sep 2009 16:12:22 +0000

Once you have zoomed your map call:

MyMap.scale_denominator()

to get the current scale denominator. This will assume a 0.00028m pixel size, so you will have to scale it to your PPI value for printable maps. Then you can calculate how far one mile and one kilometer is for your map.

I’m not sure of the relationship between zoom factor and scale in Mapnik, sorry. Try asking on their mailing list.

By: BalRam

BalRam — Fri, 25 Sep 2009 13:03:29 +0000

I am unable to convert latlong values into UTM.

Please do provide me code snippet for it too.

Thanks !!!

By: BalRam

BalRam — Fri, 25 Sep 2009 13:01:31 +0000

Hi Andrew,
May be you remembered me. You had replied my query on mapnik forum.
Thanks for it again.

Actually, I have gone throgh your way of zoom_to_box() and called zoom() function. Now its working fine.

Now, I am facing problem in measure scale in terms of kilometer or meter with current zoom level.
i.e. if I am at specific zoom level then what is scale of my map in term of kilometer; so that I can show scale factor in my map.

Getting more specific, I have to speficy zoom() in range of values 2km to 16000km and map to mapnik zoom() function which takes value in 0.1 to 1.0.

Could you please help me out of this?

Please give me some fruitful information.

Thanks!!

BalRam