[Xastir] OSM map north-america-latest.osm

[Tom Russo]

On Mon, May 29, 2023 at 12:56:55PM -0500, we recorded a bogon-computron collision of the <kc5goi at gmail.com> flavor, containing:
> I have been away for a very long time so I am sure this has been asked but
> I am not finding the answer and I am not 100% sure this is feasible. I did
> a fresh installation of 2.1.7 on a fresh Ubuntu installation. I have
> downloaded and extracted north-america-latest.osm from Geofabtrik. I am not
> seeing how to put it in service. I moved the extracted file to
> /usr/local/share/xastir/maps/Online but it does not show up in the map
> list. Am I missing a geo file or is this not supported or practical since
> it is a huge file?
> 
> Normally I try to cache an area I am going to be in ahead of time in case I
> do not have reliable cell service.

Xastir doesn't read .osm files directly.  You must process them into 
shapefiles and provide a suitable ".dbfawk" file to get them rendered properly.
Or perhaps you can download them directly as shapefiles instead.  See, for
example:

https://wiki.openstreetmap.org/wiki/Shapefiles


The "Online" directory for Xastir maps is not a collection of actual maps,
but of special files that direct Xastir to access online tile servers.  The
"geo" files direct Xastir to the appropriate server and directory on that
server to which it should connect to grab tiles as it needs them.

If you're trying to download maps to use while your station is offline, such
as while running APRS at an event, then shapefiles is the way to go.

If you're hoping to access a specific on-line tiled map set and the ones we
already have "Online" geo files for are not adequate, then you'd have to 
duplicate and modify one of the provided Online/*.geo files to get at the 
particular map you want.

At the moment I use the OSM_tiled_mapnik online map for my home station and
it is quite nice.  

If you *are* looking for offline maps and choose shapefiles, be aware that
enormous, dense shapefiles can be very slow to render, as Xastir must read
in the whole thing sometimes.  There is an attempt to optimize the access of
the file using an "rtree" data structure that keeps track of which shapes in
the file intersect the current view and only reads those in again when it
needs to, but to reduce long-term memory usage this cache is purged when your 
view hasn't changed in over an hour.  That is, it speeds things up if you're
changing views a lot, but if you have an enormous shapefile and only change
views occasionally, the first change after many hours have passed might take
a really long time to redraw as it rebuilds the index and rtree data.

For this reason, it is often good to break enormous shapefiles up into smaller
chunks.  There are some tools for doing that (gdal's OGR tools can help) but
that's another story for another time.

-- 
Tom Russo    KM5VY
Tijeras, NM  

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