Earth maps
If you are pre-generating an earth map (such as one from earth.motfe.net) there are a couple of things that you will want to keep in mind when using chunky.
Generally, existing maps do not need to be pre-generated but due to the way that these maps are created they are often missing some chunk data required by, for example, most map plugins (Dynmap, BlueMap, squaremap, etc) in order to render properly.
As a result, oftentimes you will still want to "pre-generate" the map to simply fix chunk data prior to running these other maps and tools.
To start loading an earth map, it is first recommended to enable the force-load-existing-chunks option in the configuration. As mentioned in the config comments, this basically forces the chunks to be loaded even though they already exist as will be the case for earth maps. You're not actually generating any chunks, you're just re-loading them to fix them.
After this, you just want to pre-generate as you normally would. The main difference is that since earth maps are typically not square, you will want to set the radius in both directions as appropriate.
The easiest way to do this is through the use of the corners command in chunky, as you can provide the corners of the map and have chunky automatically determine the center and radius needed to fully load the area.
Some sites like earth.motfe.net may even provide the corners already for you which makes it even easier as you will not need to figure this out on your own.
For example, you can see in the spreadsheet that the corners needed are as follows:
In the example above these are the corner coordinates low: (-36864, -18432) to high: (36863, 18431).
Keep in mind that since earth maps may be provided with different scale, the exact corners will vary. Use the corners provided with the map download or determine it on your own by inspecting the map carefully yourself.
For the example corners provided above, you would run the following commands in chunky:
chunky corners -36864 -18432 36863 18431
chunky start earth
To explain what's going on, this would set the corners of the selection to those provided, and start pre-generating the area in the world named earth. Of course, if your world is named something else, you would write that there instead. You do not need to explicitly set the center, radius, or shape, as the corners command will determine that for you automagically.
At this point, if you've done everything correctly, just wait for it to finish pre-generating, and you're done!
It is common to use a plugin or mod like Dynmap, BlueMap, or squaremap to render your earth world.
In addition to making sure the chunks have been loaded properly (as mentioned in the previous section on pre-generating) which ensures that the map is properly render-able you will also want to make sure that you have reset the map and set any visibility limits if you want them.
Visibility limits are used to avoid areas outside of your earth map from being shown on the map, and this is covered in the map rendering how-to.
Alternatively, you can also use a plugin such as VoidGen or similar to make sure that any new chunks are generated empty. It is not possible to prevent chunks from generating in any other way.
Lastly, it may be convenient to set a world border for your earth map. Since most earth maps are not square, you will not be able to use the vanilla world border but instead need another plugin or mod such as ChunkyBorder to set a rectangular border.
This is also covered in the world borders how-to, with the main difference being that you will want to add the border based on corners, exactly the same way you did for pre-generation.
With the old example above, this would be as simple as the following:
chunky corners -36864 -18432 36863 18431
chunky border add earth
The only difference here is instead of starting pre-generation with chunky start we are instead adding a border using the ChunkyBorder add-on with chunky border add.