Hacker News Reader

Comment by lucb1e | Hacker News Reader

I don't understand this part:

> In the longer term there is the option to repopulate the database used by the Standard map style so that it has access to all OpenStreetMap data tags, not just a limited few.

How does a map 'style' repopulate the database? I get that not all tags can be displayed (e.g. many businesses have a website, but you don't display that unless you want to view the business's details) so why would a map need "access" to all data tags?

I have to be reading it wrong, but I don't see how.

View on HN

There's the core OSM database (plain ol' Postgres), which contains all current OSM data plus all historical edit data. This is what you change if you click 'Edit' on OSM.

There's also the rendering database (PostGIS), which contains a subset of the current data, with freeform tags moved into Postgres columns, and with PostGIS geometries created from the raw OSM geodata. This is continually updated from the diffs of the core database. It's used by Mapnik (rendering code) to create the images you see on osm.org.

The proposed change is to add an hstore column to the rendering database, which will be populated with all the tags for each object from the core OSM database. This will require a complete reimport of the data.

Where would be a good place to start if I wanted to learn about adding additional data layers (in this case, US parcel ownership data) to OSM?

Can you explain what you mean? The OSM data base (which you can download), doesn't have "layers". It's all just one big topologically connected pile of objects.

You are free to make a local map with OSM data, and then, in your browser, or GIS software of choice, overlay anything else you want on it.

uMap is great for that:

https://wiki.openstreetmap.org/wiki/UMap

If you want to do more complicated things, try leaflet, http://leafletjs.com/

I parse that as 'There is a database. Which we use as source for the style/rendering process. It's a subset of our data, which means the style cannot even access everything we got. We might expand the subset/render from the real thing in the future'

Don't worry - it's an internal implementation thing about how the information trickles down to the intermediary database used for the rendering.

I think what they mean is that the previous Standard map style, which is produced by Mapnik, was rendered in such a way that the rendering process didn't have access to all of the possible OSM tags. But in the future they can use Mapnik to render more tags than they have in the past because Mapnik has improved in some way.

Reply on news.ycombinator.com