There are different ways of downloading OSM data. One way is using ready-made "map tiles" like you see them in your browser. The other is downloading the raw data and using a suitable vector rendering software on the device. Existing applications on the iPad use either of these methods (see [Wiki](http://wiki.openstreetmap.org/wiki/IPad) for a list of applications) but those downloading tiles are not well liked for reasons given below. __Question 1:__ This If you are talking tile data, this depends on what you mean by "street-level detail" and what area exactly you want. Let's assume you mean zoom level 17:  Let's assume you want the area inside the motorway circle in this tile:  The tile above is a zoom level 10 tile. You want approximately half of a zoom level 10 tile. Since each zoom level means 4 times the number of tiles, you can calculate like this: 0.5 tiles on z10 is 2 tiles on z11, 8 on z12, 32 on z13, 128 on z14, 512 on z15, 2048 on z16, 8192 on z17. Since you will probably want *all* these zoom levels, you're looking at roughly 10k tiles altogehter. Now the size of the PNG files varies depending on how much is on them, but for this area, I guess you'll end up with an average of about 8 KB per tile, so you're looking at a data volume of about 80 MB. The [map on the Geofabrik web site](http://tools.geofabrik.de/map/?type=Geofabrik&lon=12.46295&lat=41.89141&zoom=12&grid=1) is a good tool for getting familiar with tiles and zoom levels because you can display a tile coordinate grid on top of the map there. If you are talking vector data, then - depending on how densely the area is mapped - the same area should take about 20 MB in our raw "osm.pbf" format but you will not be able to simply download it; you will have to download a larger file (there are ready-made files for various countries or continents) and then cut out the region of interest from that file. You will then be responsible for rendering the data yourself which will *usually* encompass converting from .osm.pbf to something usable for map drawing. Existing vector drawing software like e.g. Navit does exactly that. For raw data download sources, see [the Planet.osm wiki page](http://wiki.openstreetmap.org/wiki/Planet.osm). __Questions 2 and 3:__ Downloading If you are talking tiles, then downloading this data set would violate OSM's [Tile Usage Policy](http://wiki.openstreetmap.org/wiki/Tile_usage_policy). While our tile server usually is less busy when it is night in Europe:  we would still ask people who need that amount of tiles to either produce them themselves (by downloading the raw data and setting up a rendering engine) or get them from another source. Teh aforementioned policy has links to alternative sources. If you are talking vector data, then it does not matter when you download it.

__Question 1:__ This depends on what you mean by "street-level detail" and what area exactly you want. Let's assume you mean zoom level 17:  Let's assume you want the area inside the motorway circle in this tile:  The tile above is a zoom level 10 tile. You want approximately half of a zoom level 10 tile. Since each zoom level means 4 times the number of tiles, you can calculate like this: 0.5 tiles on z10 is 2 tiles on z11, 8 on z12, 32 on z13, 128 on z14, 512 on z15, 2048 on z16, 8192 on z17. Since you will probably want *all* these zoom levels, you're looking at roughly 10k tiles altogehter. Now the size of the PNG files varies depending on how much is on them, but for this area, I guess you'll end up with an average of about 8 KB per tile, so you're looking at a data volume of about 80 MB. The [map on the Geofabrik web site](http://tools.geofabrik.de/map/?type=Geofabrik&lon=12.46295&lat=41.89141&zoom=12&grid=1) is a good tool for getting familiar with tiles and zoom levels because you can display a tile coordinate grid on top of the map there. __Questions 2 and 3:__ Downloading this data set would violate OSM's [Tile Usage Policy](http://wiki.openstreetmap.org/wiki/Tile_usage_policy). While our tile server usually is less busy when it is night in Europe:  we would still ask people who need that amount of tiles to either produce them themselves (by downloading the raw data and setting up a rendering engine) or get them from another source. Teh aforementioned policy has links to alternative sources.