Employed a switch statement that uses less SLOC.
Removed a whimsical immediately invoked function.
Stored most-recent types and time into 'recent'.

Because I am tired of looking at the repeated clumsy function expressions.
recent.time might end up undefined, so I am unable to compare it with
filters[0].time anymore. I should probably remove that one.
This avoids redundant properties of new_filter.

Because if it was part of 'recent' but not within 'options', I can skip it just
as well.
Improved local list() to use GET for small URLs.

This function still looks horrible and is useless and counter-intuitive. For
instance, if there are no keys in options, construction of the URL will fail.
Simplified control-flow in $('#export :button').click().
Removed some legacy copy-and-paste clutter.
Assigned map update to [name=limit].change().

Not that this makes the change of items word.
Removed whacky array inversion command chain algebra.
Moved map event initialization around.

I already see myself throwing the entire change-set away.
Moved map viewport initialization up one level.

Because it is independent of 'tiles_loaded'. And hopefully at the end of the
day, I get my obfuscated initialization dependencies as entangled as possible.
Lifted initialization of #filter .types and fillColors.

This also makes it look a lot better when the page is loaded.
Lifted initialization of [name=fields].