Creating external map - formats and size?

John shared this question 4 days ago


I have the whole of the UK in Ordnance Survey 1:25 as 10km squares in TIFF (not geo tiff) with TAB and TFW files for location data.

I understand i need to change the format with MAPC2MAPC for Locus.

First question:

Should i keep the map as 10km tiles (there are 2700 tiles)


merge to one large map (whole of uk, 12GB)


split into a couple of maps (<2GB?)

Second question:

What is the best format?

I see sqlitedb mentioned a lot but is GEMF more efficient?

And lastly

I have converted one tile as a test and its size as a TIFF was 400kb + 2kb for TAB. Its size then became 2.7mb as a sqlitedb and 2.2mb as GEMF.

Is this growth normal? The TIFFS are already 12GB total.


Comments (3)


Dear John

firstly I hope that you have right to use OS data.

q1 - I would suggest to split data into couple maps, let's say about 500 MB. I think that it'll be better for generation and possibility to copy only several maps into device

q2 - please use sqlitedb. GEMF should be effecient (when it comes to size of the map) but .sqlitedb is proven for several years and also for large maps

q3 - well It depends... it depends on number of zoom levels you want to generate (every zoom level increase 4x the size of map), it depends if mapc2mapc somehow optimize map tiles for sqlitedb format (this is question for John Thorn - the developer of mapc2mapc)

BTW: I'd only mention that you can use/purchase Landranger or explorer OS maps in the Locus Store or use Great Britain map from John Thorn that combines OSM and OS open data

Thanks, Petr


Thanks for the Info Petr.

I will go with your suggestions.

I do not understand what zoom levels are for so i will search for this info. Any links to hand?

Yes, i already have OS Explorer 1:25 so do not want to buy. They are good alongside OSM.

I did not know about John Thorns already combined map. Interesting



the zoom-levels are basically scales the map offers a good explanation: A zoom level determines how much of the map is visible: at zoom level 0 you see the whole world, at zoom level 16 you could see a small road. This data is stored in a quadtree data structure. The zoom level also affects the size of the vector tiles that are loaded.

at You can also check the

I would suggest max zoom-level = 15 for 1:25000 map

Regarding John Thorn vector map - please check the Great Britain All in the Locus Store.

Thanks, Petr