Size matters -- So Ya wanna big pic? Solution:
Newbie here. Not sure if anyone is still on this thread... Ok, I had the exact same dilemna - I wanted a fully scale-able and omnidirectional-scrollable OFFLINE map of London on my iPhone 3G. Specifically, I wanted a nice-resolution scan of a printed London travel map.
DO THIS:
1) open your large-format RGB photo/scan/etc raster image in Photoshop*. Save it as a "high-quality-print" Photoshop PDF format
2) upload the Photoshop PDF to your iphone using FileMagnet App (worth shelling out the $4.50 even if it (sometimes) crashes after 🙂 the upload)
3) DONE (the image will be accessable via FileMagnet). Looks dandy, Andy.
* using Photoshop CS3 on a Mac... not sure if there's an equally good imaging program that will do as nice a job... I tried creating a PDf using PaintNet (free) on my Compaq laptop ("printing" via CutePDF Writer (free)), but the end iPhone-display-results were not nearly as nice a Photoshop's PDF... even tho I used the same source raster image for both.