How can I choose the zoom level for my map?

According to both Notch's Twitter (no link) and the wiki, maps have some kind of settable zoom:

A zoom level, which will somehow be decided at the time the map is created.

I have no idea how to set this. Anyone know?

EDIT: based on fjdumont's answer, how is it calculated? Is there anything I can do (such as craft it in a certain place) to give it a zoom level close to what I want?

Solution 1:

You can zoom map files, but you have to do it by editing your NBT files. This answer is thanks to this redditor:

If you're willing to dive deep into the NBT files, you can adjust the map's center and zoom levels. Just don't screw with dimension (locks the map) or width/height — it doesn't work. The files are under <map-name>/Data/map_X.dat, where X is the map number.

You'll need to use an editor like NBTEdit to edit the files.

Solution 2:

From version 1.4, you can zoom maps in game, as the whole process of map-making is changed:

First, a blank map is created

This blank map will not start recording immediately, as maps previously did.
The blank map can be activated by right clicking it, which turns it into a map at the most zoomed in level (1 px/1 block)
To scale the map by a factor of two, take the map and recraft it as follows:
Each time this is done the map will scale out, so from 1px -> 1 block, to 1 px -> 4 blocks, to 1 px -> 16 blocks and so on. This can be done a maximum of 5 times. Maps cannot be scaled back in, only out.

Solution 3:

Looks like yes, this is the work of a mod. Here's how you can do it:

Download NBTedit from here
Unzip the ZIP file
Run NBTedit
Click File -> Open
Navigate to your save folder
Go to the "Data" folder
Open the map_0 file. If its not map_0 you want to edit, choose the right one.
Expand the "data: 7 entries" branch
Change the "scale" value to the one you want. I chose 1, but it can be anything.

Solution 4:

I have made a program specifically for map item files. You can find it here http://sourceforge.net/projects/mapitemedit/

You can edit your zoom level, map coordinates, even change the picture data.

Solution 5:

When crafting a zoomed out map with eight pieces of paper, shift-clicking on the output map in the crafting table does not make a newly scaled map

in the bug section of the wiki

http://www.minecraftwiki.net/wiki/Map_(item)