When read large map tiles file at format, zMap may suspends on "Analysis Map Tiles" process or crash. The problem is caused by the database index for these files are not design for non-continuous zoom level and the conversion process is quite resouces-consuming on iOS device. To solve this problem, you will need pre-process for the map tiles file on the computer by Firefox with extension SQLite-manager (http://code.google.com/p/sqlite-manager/)
Start SQLite-Manager at Firefox by Tools>SQLite Manager.
Open the map tiles file by Database>Connect Database
Press "Execute SQL" view and type "create index if not exists indexZ on tiles (z, x, y,s)" then press "Run SQL" to create database index. The progress may take several minutes depends on the file size. The new index indexZ should show at left pane when finish.
Select "IND" index and go to "Structure" view. Press "Reindex" to renew IND index and do again for index "sqlite_autoindex_titles_1".
Select "Database>Compact Database" to compact map tiles file.
When you open the file at zMap at the first time, disable "Auto screen Lock" of your iOS device to prevent zMap switch to background task will be help too.
(Reference data:3.2GB sqlitedb (RMaps) file will takes 150 seconds for "Analysis Map Tiles" on iPhone4)