OpenStreetMap

More work on Bolder

Posted by pnorman on 8 August 2018 in English (English)

This is a mirror of a post on my blog.

After the birds of a feather session Richard Fairhurst lead at State of the Map, I was motivated to continue some work on bolder, a client-side style I've been working on.

While I was working at the Wikimedia Foundation, I developed brighmed, a CartoCSS style using vector tiles. Wikimedia decided not to flip the switch to deploy the style, but the style is open source, so I can use it elsewhere. Making this decision, I spent a day implementing most of it in Tangram.

Bolder example image

What's next?

I've got some missing features like service roads and some railway values to add, then I can look at new stuff like POIs. For that I'll need to look at icons and where to fit them into colourspace.

There's a bunch of label work that needs to be done, what I have is just a first pass, and some things like motorway names have big issues, and ref tags still need rendering. Label quality is of course a unending quest, but I should be able to get some big gains without much work.

Richard is planning to do some work on writing a schema, and if it works, I'd like to adopt it. At the same time, I don't want to tie myself to an external schema which may have different cartographic aims, so I'll have to see how that works out. Looking at past OpenStreetMap Carto changes to project.mml, I found that what would be breaking schema changes on a vector tile project are less common than I thought, happening about once every 4-6 months. Most of the schema changes that would have happened were compatible and could be handled by regenerating tiles in the background.

Comment from imagico on 8 August 2018 at 18:03

In your sample rendering the drawing order of the roads looks odd, kind of random.

Regarding styling, i have to say at the moment i don't really see where it aims at. It to me pretty much looks like an OpenMapTiles/MapboxStreets look-alike in slightly different colors but without a distinct cartographic direction. I know this is still in an early state but i would contemplate the question of cartographic goals before putting too much work into it. Starting with a clear vision design wise can help you a lot.

Comment from pnorman on 8 August 2018 at 19:14

In your sample rendering the drawing order of the roads looks odd, kind of random.

It is in fact random, because Tegola is trying to do some things it shouldn't with queries which makes ORDER BY hard to use in queries. This is similar to how a bad Mapnik query can result in a sequential scan on start-up. Because Tangram is a lot more flexible with ordering than Mapnik thanks to its GL origins, I could avoid needing to ORDER BY within a layer by including a z ordering within the query output, but I don't like this technique as much.

Road ordering is important for using the map, but doesn't impact designing the cartography of the rest of the features, so I'm leaving the issue aside until it becomes more important or the Tegola bug is resolved.

I find it easier to express cartographic design once I have a baseline to work on. A few things I want to experiment with are bringing back stronger road colours, stronger casings, and how much I want to vary road thickness by classification.

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