How is map scaling for missing zoom levels?

Martin M shared this question 36 days ago
Answered

As I am struggling with IGN France offline maps...

IGN france maps seem to be defined for the following zoom levels mainly

5 World

7

9

11

13 50k maps

15 25k maps

Even levels seem to be upscaled versions (eg. 14 is an upscaled 13 (50k) map).

As it is so, it seems redundant to download even zoom levels (as they contain no extra information, just waste space).

Question: If I download zoom levels 13 and 15 only, what will LM show me with zoom 14?

Will it be an upscaled 13 or downscaled 15? For offline maps, it seems to be upscaled 13. Is this always so (or is this user selectable)? Is the behavior identical for online/offline maps (some weird effects there, see my related post)?

Thanks for the clarification!

Martin

Comments (4)

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Dear Martin,

the loading and scaling the map tiles can be different for online and offline maps.

IGN Online Maps - Locus asks the IGN map server for data for every zoom level. When you zoom-in to ZL14 Locus loads data from map server without any re-scaling. It's on IGN what data serve. You're right that you get re-scaled 50k map but this maintained by IGN map server.

Any offline map with missing ZL - Let say that you download ZL 9, 11, 13, 15. When you zoom-in to level 14, Locus loads data for ZL13 and re-scale it. Users can't influence what ZL is used for re-scale.

I'd like to also mention if you decide to download a map without any ZL, please do not mix the ZL ranges in the map file. I mean do not use several supplementary downloads with different range of zoom levels. Locus would load such a map correctly, but I suggest to not mix the ZL.


Thanks, Petr

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Dear Petr,

thanks for the explanation.

What do you mean by "download a map without any ZL"? Do you mean just one ZL like 9 or 15?

Anyway, that's probably a bit theoretic. What I'd like to do: Download whole France with ZL 5,7,9,11,13. That's 112903 tiles total, a bit over 1 GB. Then, for multiple, different areas ZL 15 on top (because whole France ZL15 would be 16 GB). This should work? I could add the even ZL also (6,8,...), but as they are scaled only, I am not sure if there is any benefit.

Regars, Martin

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Dear Martin,

I'm sorry, I wanted to say that you can skip specific zoom-levels and download, for example, ZL 5,7,9,11,13.

Your plan should very likely work. Anyway, I wouldn't suggest it. Please consider usage France LoMaps maps from Locus store together with IGN maps. LoMaps have smaller size then online maps (whole France to zoom-level 20 has about 2.5GB), the appearance can be influenced by themes. You get also offline addresses and POI database. Please see link below for more info about LoMaps https://docs.locusmap.eu/doku.php?id=manual:user_guide:maps_locusmaps

I would download IGN only for the areas you're really interested in. I'd use LoMap maps for general usage and combine them with IGN for the specific areas.

Thanks, Petr

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Dear Petr,

of course I am using LoMaps. Actually I mostly use LoMaps (except for MTB where openandromaps elevate/MTB show much more detail). For France however, I like the extra information the IGN topo maps have (of course I have the french LoMaps as well). As a matter of fact, the main reason I am using LM is because it supports the IGN France subscription (and mytrails announced to shut down soon). I just don't want to download fresh map pieces every time I want to visit France, so I'd rather download as much as possible and let it be. S10 has 128 GB of storage so I don't mind spending a few GB.

Lets hope the official map institutes IGN France and Swisstopo will at some time switch to vector maps as well so we don't need this gigabyte tile heaps anymore. Probably until then (=distant future) OSM maps improved that much so we don't need the official topo maps anymore.

Regards, Martin