Rendering Effective Route Maps: Improving Usability Through Generalization Maneesh Agrawala, Chris Stolte Stanford University Presented by Ken Deeter

General Idea Automatically generate a route map that has the same properties as a hand drawn map. Hand drawn maps: –Exaggerated Lengths (non-constant scale factor) –No irrelevant information

More Specifically Constant scale factor –Road lengths on a conventional map vary in several orders of magnitude => small roads and neighborhoods are hard to navigate with large maps Information irrelevant to navigation –Names of locations, places, cities, etc. that are all far away from the route –Takes up space that would be otherwise useful for showing crossroads and relevant landmarks

Cog. Psych. Research Recipe for an effective route map: –Clearly communicate all turning points NOT: –Correct lengths –Correct angles –Correct shape

Generalization Techniques Generalize Length –Use more space for short roads, less for longer ones. Distribute based on importance, not physical length Generalize Angle –Align roads or make room for others Generalize Shape –Navigator doesn’t need to know roads shape. –Simpler roads are easier to differentiate on a map.

Route Map Generation Pipeline Input: Route data Process: –Shape simplification –Road Layout –Label Layout –Context Layout –Decoration Output: Map image

Shape Simplification Simplify roads but with specific constraints –No missing intersection –No false intersection –No wrong turn direction For roads where shape is important (curvy such as highway ramps) be more conservative.

Road Layout Formulated as a search in the space of all road layout configurations. –Simulated annealing to find optimal layouts –Requires layout scoring function, and perturbation function Perturbation modifies a length of a road by up to 20% or orientation by 5 degrees

Layout Scoring Penalize for short roads Penalize for change in ordering of length of roads Penalize for change in orientation from original Penalize for missing and false intersections (many tricky details.. See paper for speficics) Penalize for bad shape: if orientation of start and endpoints is different, or if they are too close

Remaining Layout Label: Tries to layout labels deterministically, then resorts to search for conflict resolution Context: Adds crossroad and landmark information Decoration: global orientation arrow, explicit turn points,

Output Image Size Estimate at first by using simple distortion. For small displays find orientation that takes best advantage of devices vertical scrolling capability (most routes are not square) –At the same time try to keep north as up –Resolution: 200 pixels for routes with 10 steps + 10 pixels/step

Evaluation 2200 users, voluntary feedback (self- selected) More than 95% percent said they would use the system

Drawbacks Layout still fails in some cases –Random search does not converge to optimal layout –Sometimes impossible to stay within all constraints Not useful for long trips Not useful for when people get lost PDA displays more likely to have problems of overlapping labels

Demo at mapblast.com