Allow Ctrl-Arrow decrease the pan increment

[prushforth]

Make it easier to target smaller features using keyboard + graticule

[Malvoz]

2 observations:

• I've been looking into gestures and keyboard controls recently, and it seems none of the UCR reference tools use the ctrl modifier key for anything, for some reason. So if pursuing this it might be worth investigating if that may be an issue.
• AFAICT with Feature Indexing this would potentially not be necessary.

[ben-lu-uw]

In the _onKeyDown function in Leaflet they return if the control key is pressed, not really sure why though.

Maybe cause Chrome has a ctrl + arrow shortcut set for moving tabs but it does not seem to work or do anything for me?

I did try adding this feature here https://github.com/ben-lu-uw/Web-Map-Custom-Element/tree/ctrl_pan and it seems to be issue free for me

[Malvoz]

Google Maps uses the shift modifier to decrease the pan increment, however Leaflet already uses that to increase it...

[prushforth]

I tested powerpoint just now and ctrl-arrow doesn't appear to do anything different than just arrow by itself.
Shift-arrow increases the size of an object, and ctrl-shift-arrow also increases the size but reduces the size increment step.

Ctrl-scrollwheel or Ctrl-+/- changes the magnification of a domain in chrome.

Ctrl-arrow skips a word in most text editors, so increases the increment of cursor movement.

Let's dig a little more to see if there's anything arguing against using ctrl-arrow for decreased pan increments.

[Malvoz]

Let's dig a little more to see if there's anything arguing against using ctrl-arrow for decreased pan increments.

Ability to rotate map will need a modifier too.

[ben-lu-uw]

Let's dig a little more to see if there's anything arguing against using ctrl-arrow for decreased pan increments.

Leaflet/Leaflet#2368