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How to export a huge map in A0 format size, with visible background image without loss in details? (street names and house numbers should be visible)

Parameters of the network I want to export for printing:

  • area ~ 600km2

  • perimeter ~ 100km2

  • background = OSM predownloaded via SASplanet, zoom level 18

Required output:

  • A0 format size file for printing
  • Added polygons of the districts (gpkg file format)
  • Background map without dramatic compression,
  • Background clipped to the extent of polygons
  • Numbers of buildings should be clearly visible and easily recognized same for the street names.

I have tried different settings for export via layouts, but either quality is not clear and characters not possible to recognize, or after clipping of raster by polygons even with checked option to preserve image resolution the quality drops significantly

I use QGIS for this task because I need to add polygons to the background map to show borders of the city districts.

Or are there any suggestions for another way to achieve the same result?

Vince
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Alexander Fediushyn
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  • You mention TIF in your question title, but not in the question body - is TIFF required? What about PDF? – Midavalo Oct 03 '21 at 23:01
  • not really, actually everything will work, until i can print it in print center) even better – the less it weights – the better, considering the mentioned requirements of course – Alexander Fediushyn Oct 03 '21 at 23:39

1 Answers1

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Some approximate numbers: A0 paper is about 1m each side, a 600 sq km area is about a 25x25km square. So your printed map will be at a scale of 1:25000, more or less.

I'm not familiar with SAS.Planet, but a Level 18 tiled basemap is 60cm per pixel at the equator (see https://wiki.openstreetmap.org/wiki/Zoom_levels). Labels on the map will (usually) have been rendered assuming 96 dpi. So a 12 pt "fairly large" label will be 96x12/72=16 pixels high, so would be about 0.60*16=10m in map units. At a scale of 1:25000, this will be 0.4mm high when printed and so not legible.

All of this is true at the equator, and needs to be scaled by cos(latitude) elsewhere. And it won't quite be right given the actual geometry of your region, and because font sizes aren't actually 12pt. But it does show that -- unless you do fancy stuff with higher-dpi tiles -- you need to probably use Level 15 or 16 tiles for the background map, rather than Level 18, to be legible. Labels and symbols will then be 8 or 4 times (respectively) larger, and so you have a hope of them being legible.

You can then clip the raster by polygons, etc.

If you need other details shown only on Level 18 OSM maps, you can try some of the suggestions at Making street names visible on OSMM WMS, increasing resolution of WMS map at constant scale (Scale Dependent OSMM -SV) (though this is written in a different context, namely WMS). You may do better using vector tiles, e.g. with the MapTiler plugin (this is exactly what it was designed for, but it may be cost-prohibitive for your application!), or by downloading and custom styling the vector data OSM uses for your region, most likely from government sources. That's what I do for my maps in Canada.

Houska
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    wow! thank you for that detailed answer, appreciate it!) never ever thought about it from that point of view. i'm not actually studied GIS or whatsoever, but indeed use it and learn it during my work) i will try to make use of your answer! – Alexander Fediushyn Oct 04 '21 at 02:26