One of the problems any developer has is of course access to high-quality map data that can be displayed offline. Map data used to be very expensive and therefore only available to large development companies, however, today there exists an open source map initiative named Open Street Maps and useful API´s based on that data, such as Cloudmade.

We use the Open Street Maps data for all our offline map-data on the mobile devices, and can thus effectively deploy a mobile application with offline map-data from anywhere in the world. Combined with our experiences as mobile developers we can publish such a mobile application for literally hundreds of devices simultaneously.

J2ME devices

Clarification: J2ME is a software development tool for mobiles that is based on Java and managed by Sun (which was recently purchased by Oracle). It is the most ubiquitous tool to date and we use it to make Mobileguide clients for Nokia, Sony Ericsson, Samsung, Blackberry and numerous other devices.

J2ME is generally resource limited, especially when it comes to memory.  Even numerous new devices offer J2ME applications only around 2 MB of working memory, and a maximum application size of 1 mb, which is a severe limitation especially when it comes to displaying vasts amounts of map data. Given these constraints for the majority of devices, the only realistic way of displaying vasts amounts of map data is by working with the map data in vector form (coordinates and not bitmaps) and then using the graphic primitives of the device itself to draw the map. This vastly reduces the size of the size of the map, especially when it is combined with tiling techniques for the vector data. With this approach we managed to reduce the total size of the map data for the whole of Iceland (streets, coastline, street-names and geographic location names) to 750kb, down from approximately 10 Megabytes of raw XML data.

The end result is not as visually pleasing as a bitmap image taken from Open Street Maps, but the map interaction is fast even on slow devices, you can easily navigate by it, and it is completely offline so you never need to worry about any costs.

Screenshots from an average Sony Ericsson emulator

Apple & Android

With these platforms we are not plagued by the same constraints as for J2ME, the devices that are supported by these platforms are true smart-phones with extensive processing power and memory. The API´s behind these platforms are also more modern, with more features and plugins to 3rd party services. In version 1.0 and 1.1 of the iPhone version we used the RouteME API to display Open Street Map data.

Data from Open Street Maps displayed on the iPhone

For version 2.0, we cache the bitmap tiles directly on the device itself for the best offline experience. The whole bitmap data for Iceland is in the range of several hundred Megabytes, but by allowing the user himself to hand-pick which sections of Iceland and removing some tile layers in-between, we manage to reduce the size to a reasonable level for these devices.