zoom 9 tile has excessive landuse, other layer details

[nvkelso]

http://vector.mapzen.com/osm/all/9/245/166.topojson?api_key=vector-tiles-HqUVidw

There are many tiny landuse features included in this tile.

• The large ones should keep their names and independent existence.
• The smaller ones should loose their names and be merged (like what we started doing in the roads layer in v0.7).

[nvkelso]

Download: 9:245:166.topojson.json.zip

[nvkelso]

Separate tile previewed in QGIS:

22.json.zip

For instance, all the Urban Area polygons from Natural Earth at the same min_zoom and sort_key could be merged.

[nvkelso]

I suspect the roads and boundary layers need additional geom simplifying.

We could also strip some properties off the boundary layer at low zooms (like name and the name variants) at zooms less than 8 as the zoom isn't large enough to provide screen space to do the labeling.

[zerebubuth]

Tracking changes for the linework in roads and boundaries layers in #641 - no need to conflate that task, which is about altering a threshold for a feature we already have, and this one which is about adding an entirely new feature.

[nvkelso]

Establish some scale ranks for landuse

From queries.yaml, these are already applied, but the CSV is empty now.

The sizes will be similar to how buildings.csv is setup, but you'll use some of the area thresholds from other filters.

You'll need to create a new merge function, similar to roads and buildings, using the scalerank and the tier values.

[nvkelso]

See issue #473 for landuse tiers, and scale rank recommendations (there are pasted filter values there).

[nvkelso]

Perhaps use #202 to set different area threshold per kind? @rmarianski how would @okavvada do that?

[rmarianski]

Yes, we can use several approaches, and even all of them together. I'll put in pointers to the different pieces.

1. Assign scalerank using the spreadsheet.
2. To drop features that aren't a minimum size, update the mz_min_pixels spreadsheet. We already have a transform configured that drops the features that don't meet the mz_min_pixels threshold, so updating the spreadsheet is all that's required. Remember to restart tileserver after making updates to this file.
3. Here's the building merge transform. We also have one to merge roads, that is slightly different.
   Sounds like the criteria here is slightly different, in the sense that we want to drop the name property but only for features that don't meet an area threshold, but the rest should be similar to the buildings merge.
   I'd suggest making a new transform to get this working first, and then perhaps in a separate future issue we can see if it's possible to unify all these merges together.

By the way, if we're going to merge, it might be safer not to drop any features.

[nvkelso]

Wow! This is fantastic – I'm seeing improvements in less features and smaller file sizes at all zoom levels!

But at low zooms we still have individual tile features for national_park features but I expected to only see merged "generic" polygons within the kind.

Since work in this issue gave us a huge win and additional merging is not backwards incompatible, let's track additional work in #1033.