Panoramascope: Augmented Reality uses worldwide terrain data from NASA to compute the skyline as seen from anywhere on the planet. This is superimposed on the view from the iPhone's camera, oriented using the compass, with labels to identify mountain peaks and other features.

So when you're stood on top of a peak, you can now identify all the surrounding features. Or if the cloud comes down, you can work out what you should have been able to see.

When you're away from the mountains you can search for viewpoints and compute their views - great for trip planning, or just for armchair travel.

Panoramascope: Augmented Reality can also be used in flatter parts of the world, and marker layers are provided for features including tourist attractions and pubs (marker data is mostly from OpenStreetMap.org). However, the most impressive results are definitely obtained in mountainous areas.

In the US and Canada, Panoramascope works with the app Topo Maps, if you have installed that app, to show the view from a point selected on the map.

Because the compass is required, this app only works on the iPhone 3GS.

Note that the 17+ rating is purely because the app's help screen could be abused to provide uncensored internet access.