[Talk-GB] Idea - OSMUK walkers' map application -- -& server

Andy Townsend ajt1047 at gmail.com
Fri Dec 11 13:40:09 UTC 2020


On 11/12/2020 09:59, Nick Whitelegg via Talk-GB wrote:
>
>
> In the early stages I think we could run it on cheap hosting hardware, 
> like most projects in the OSM ecosystem. I suspect for a while usage 
> would be light and limited to those in the OSM community. I use 
> Hetzner for my hosting (OpenTrailView, Hikar, MapThePaths) - I pay 
> around EUR 19/month but that is for a larger system that has to deal 
> with the whole of Europe rather than just the UK.
>
> https://www.hetzner.com/cloud?country=gb 
> <https://www.hetzner.com/cloud?country=gb>
>
> The second-lowest spec of these, the CPX11 is giving you 2GB RAM and 
> 40GB disc space for EUR 4.19 a month. OK we'd need more than that long 
> term, but I suspect that would get us going in the early stages.


That'll depending on what you want the server to do, I think. For an OSM 
Carto Map style with automatic updates and reasonable performance you'll 
probably need > 6Gb memory for the whole of the UK these days.  Maybe a 
CX31 at €11 per month (i.e. about the price of a couple of pints and a 
"substantial" pork pie for those in tier 2)?  
https://map.atownsend.org.uk is a CX41 I believe, and renders Mapnik / 
Carto CSS map tiles that cover UK and Ireland. It could probably include 
another "medium sized OSM country" in the same map style as well without 
too many problems.


On the question of "could we show feature X" (e.g. "cycleways with 
foot=yes" different to "cycleways with foot=no) the answer is 
technically yes, but you need to decide which subset of features you 
want to show because there simply aren't enough ways of visually 
distinguishing things that users can actually tell apart, especially 
when combined with other features.


As an example, have a look at the legend at 
https://map.atownsend.org.uk/maps/map/map.html#zoom=16&lat=-24.98988&lon=135.10862 
.  That shows:

  * designation (public footpath / bridleway / retricted byway / BOAT /
    UCR / none)
  * width - either "narrow" (not wide enough for a 4 wheeled vehicle) or
    "wide" (wide enough)
  * trail_visibility
  * some surface information (unclassified unpaved roads rendered
    differently to paved roads)
  * tunnel yes/no
  * long ford yes/no
  * bridge yes/no
  * embankment yes/no
  * long distance foot / bicycle / horse riding routes
  * access=destination and =private viewed from a pedestrian perspective

and of course combinations of the above.


It does not show:

  * explicit OSM keys (e.g. footway/cycleway/path/bridleway)
  * explicit OSM access tags (e.g. "foot=yes or no on a cycleway")
  * undesignated cycleways differently from other undesignated paths

In order to one of those (for example just "displaying cycleways as 
cycleways") you'd need to remove something else that's already rendered, 
otherwise users won't be able to tell features apart.


Assuming that people are planning to go down the mod_tile / Mapnik / 
Carto CSS route, I'd suggest:

 1. decide what zoom levels you want, which will influence exactly which
    software to use
 2. deciding where to start from (e.g OSM's Standard style, mine, or a
    different one altogether)
 3. deciding exactly what you want to change
 4. make those changes,
 5. see what "unintended consequences" have occurred
 6. fix those and iterate round until happy

Assuming you can deal a couple of hours overnight downtime while the 
database reloads I'd suggest doing most of the "deciding what to show as 
different things" work in lua and the "deciding what to show it as" in 
Carto CSS.  It's much easier to understand and to maintain.


With regard to the "boring bit" (scripts to load databases, keep 
databases up to date etc.) most of the stuff used by 
https://map.atownsend.org.uk is public (links to everything are at the 
top of the changelog).  Much of the rest (e.g. automatic https 
certificate renewal) is standard and is documented in 1000s of other 
places around the internet.  If anyone wants any help or advice with any 
of the above please just ask.


There may be a temptation to think "the end goal is a phone app , so 
actually we probably want to look at $some_other_technology instead".  I 
would strongly suggest following a well-trodden path first while so that 
the things that are new to whoever is doing this are have 
well-documented solutions.  I haven't yet found a vector tile stack that 
is (a) well documented and (b) free of vendor lock-in that could go on 
https://switch2osm.org/serving-tiles/ yet, for example.  Once whoever is 
doing this is familiar with things, trying something a bit more 
off-the-wall will be more likely to work without everything breaking.


The biggest requirement is for someone to actually commit to doing the 
work to set something up - nothing will happen without this.  If OSM UK 
are happy to fund a server, and for it to fit in their DNS somewhere 
then that's one less expense to worry about - but someone still needs to 
do the work.


Best Regards,


Andy




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