Personalised maps show the view from the street


By Colin Barras (Image: Floraine Grabler/SIGGRAPH) Finding your way across an unfamiliar city is a challenge for most people’s sense of direction. Software that generates personalised maps showing only relevant information, and carefully chosen views of selected landmarks, could make disorientation a thing of the past. Thanks to online services such as Google Maps and Microsoft Live maps now contain more information than ever. It is possible to toggle between a regular schematic, a “bird’s eye view” that uses aerial photos and even three-dimensional representations of a city’s buildings. Those multiple perspectives can help users locate themselves more accurately. But there is a risk of overloading the viewer with information, says Floraine Grabler at the University of California in Berkeley. “When the maps show every building, every street, it’s very difficult to find specific sites,” she says. They are also unsuitable for using when actually walking around. Grabler has built software to let people generate maps for places they’re going that display just the essential information – projections of landmark buildings, along with clear views of the major roads. Grabler’s team at Berkeley, working with researchers at ETH Zurich, used a perceptual study of San Francisco from the 1960s to help identify which landmark buildings to include on a map of the city. They found that landmark buildings came in three varieties. “Landmarks can be semantic – for instance, a theatre is a cultural landmark,” says Grabler. “There are also visual landmarks, with a colour and shape that makes them distinctive, and structural landmarks with a strategic position: on the edge of a square or at an intersection.” These categories were used to give each building in San Francisco a rating on the basis of its score in each of the three categories. Only those that scored above a threshold value were then displayed on the final map. When generating a map, the user can choose to display those landmarks in one of two ways. They can be displayed as straightforward three-dimensional depictions, but that masks the buildings’ facades. To provide the user with more information, Grabler’s team added an oblique projection option, which shows all visible sides of the building. Although the buildings look distorted compared with a regular three-dimensional depiction, it is possible to see all the facades a building presents to the street, including both facades for a building on a corner. But buildings depicted this way can hide some streets. This is avoided by widening the map’s roads, and shrinking the height of the buildings so that roads remain visible behind even tall buildings. The user’s final decision is to choose the purpose of their map. On a shopping map, all the major shops become semantically important and are included on the map. A food map, by contrast, will show fewer shops but more of the city’s restaurants. Grabler’s team has yet to test their maps on San Franciscan tourists,
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