Feature Addition: Ability to have custom mbtile overlays

[brendancol]

Hey,

I wanted the ability to create an overlay layer in tilemill which I could then overlay with field papers. The basic flow is the following:

• User must be logged in
• User clicks "Extend" Nav
• User clicks MBTiles Uploader Tool
• User uploads .mbtiles file to account
• User selects "Make"
• Make Step-1 has 2nd the option to use custom uploaded tiles
  
• Make Step-2 would now have a separate dropdown to control the overlay layer:
  
• Overlay selection would carry through to atlas pdf

I have implemented the bulk of this, but am still testing.

One debatable issue I ran into was the empty tile. Because the overlay mbtile mostly be empty tiles to let the base layer shine through, I commented out the empty tile logic:

So this is NOT ready to officially merge to master yet, but is functional and I wanted to get some feedback.

Thanks.

[almccon]

I doubt any of us at Stamen will have a chance to look at this for the next few weeks, but I just wanted to say that this idea is great! I look forward to testing it later!

[brendancol]

Oh yeah. Totally understand. I will be trying to work out any kinks and committing changes as I go. Happy Holidays to all