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CityMap

CityMap allows you to browse and search quite a large map; the practical limit, because of AppStore download limitations, is about 10Mb. CartoType's compact CTM1 data format enables large cities like London, Paris and New York to fit comfortably into that size - including every street, and most bars, restaurants, car parks and other points of interest. Storing the map offline, that is, keeping it locally in the device rather than downloading it over a data connection, means that maps can be drawn faster and the user pays no data access charges.

iPhone applications are written in Objective C, not C++ but that problem was relatively easily overcome. Objective C applications can use standard C++ code. Only a simple Objective C wrapper was needed to connect the core CartoType library to the iPhone app framework and UI. Data was downloaded from the OpenStreetMap database using the extended API. For some maps, data was downloaded from the CloudMade server and extracts were created using a Perl script. The data was then passed through CartoType's standard data conversion tool, generate_map_data_type1, which reads OpenStreetMap's XML data and creates a CTM1 file.

Greys Mead decided to use two different style sheets. A full, complex style sheet is used normally, but for increased speed when panning in perspective mode a simpler style with no labels is used.

CTM1 files include a placename index designed for high-speed searching, so adding the search facility was very easy. Found objects are highlighted by drawing them as a separate layer, specified in the style sheet, using an orange outline and a transparent yellow overlay. CartoType makes it very easy to customise maps at runtime by adding extra objects and extra map layers. This extra data can be drawn using all the graphical and typographic features that are available for normal data.

CityMap has been released for London, New York City, the San Francisco Bay Area, Los Angeles, Birmingham (UK), Liverpool and Manchester, and Central Scotland. More cities will be released soon including Paris.

In June 2010 a new version of CityMap London was released with complete searchable postcodes derived from Ordnance Survey Code-Point Open data.