Position Paper
on
Rendering Effective Route Maps:
Improving Usability Through Generalization
Maneesh Agrawala, Chris Stolte (2001)
by
Chirstian Baar, Michael Pannier
Cognitive Systems - WS 2012/2013
7th December 2012
1
Motivation
Computer generated Maps are very
precise and contain lots of information.
Several
cartographic
generalization
techniques are available in order to
improve the clarity of maps or emphasize
special information. Distortion, simplification and abstraction are commonly
seen on political, economical public
transport maps. Yet, few to none of those
techniques are used for automatically
generated route maps.
Figure 2: Route map rendered by a person
On the other hand, route maps drawn by
hand focus on the route itself and not on
the whole environment along the way.
Generalization techniques are used subconsciously to show important information
for navigation.
2
Figure 1: Route map rendered by a standard
computer mapping system
So, in a typical computer generated route
map the route is highlighted by coloring.
The shape of the route remains the same.
Since the scale of map is kept and the
lengths of the roads vary some roads
might disappear. In addition, there are no
differentiations between necessary and
supplemental information displayed on the
map. Therefore, additional information
could distract from or even occlude
important navigational information.
Idea
In order to introduce their automatic route
map design software called LineDrive
Agrawala and Stolte developed a set of
route map generalization techniques to
improve computer generated route maps.
Firgure 3: Route map rendered by LineDrive
3
Research
According to Agrawala and Stolte, cognitive psychology has identified the most
important navigational tasks. First, a route
can be understood as a series of turning
points. A turning point consists of two
major elements. They are a pair of roads
crossing and a turning direction. Further,
additional information such as landmarks,
labels and distances, are of orienteering
help, too.
4
data is forwarded into the pipeline. The
LineDrive-pipeline has five steps, which
are changing the route map from an
ordinary to a simplified route map.
Cognitive Model
After identifying the main tasks in the
cognitive model of navigation and their
necessary information three generalization
techniques for route maps were implemented.
Length generalization uses distortion of
the roads along the route. Former invisible
roads are extended and long roads are
shortened. The ordinal structure of the
roads is kept. Thus, longer bits of the route
on an interstate or highway for example
are still displayed longer than short lanes
within a town.
Angle generalization widens tight angles in
order to make space for labeling and
better readability.
Shape generalization makes the route
easier to comprehend. By removing inner
knots of the route's the overall shape of
the route is simplified. Nevertheless, the
main shape of the route has to be kept.
5
Realization
Linedrive uses a pipeline for rendering the
route. At first, the request for the route
data is made via a route finding service
using a geographic database, which in this
case was MapBlast. After that the route
Figure 4: Block diagramm of LineDrive-pipeline
First, the shape of the route is simplified.
In the shape simplification-step the
amount of road segments is reduced,
while the overall route's shape is kept, and
its recognizability is improved. During this
process false intersections mustn't be
introduced. Simulated annealing is used to
determine, which simplified layout is best.
This heuristic optimization technique
allows local minima, and not every
possible layout has to be tested. At start
an initial layout is scored, and until a
termination condition is not reached the
layout is changed, scored and compared
to its predecessor. Either it is better and
becomes the new layout, or it is worse. In
this case a certain impairment is allowed
according to the amount of steps until this
point. This means that those granted
impairments become minor over time.
The goal of the Road Layout here is to
determine the length and orientation for all
roads, such that all streets are visible and
fit into the screen of a predefined image
size, e.g. the 600 x 400 pixel screen of the
“Palm PDA” which was used in the design
phase of Line Drive. In the first step of the
route layout the length and orientation of
the roads is set. In order to fit into the
screen the long roads are made shorter
and for more details the short roads are
extended in this step. It is important in this
step that the shape of the route and the
ordinal order of the streets are still correct.
Both missing and false intersections can
be extremely misleading so in this step the
goal is to correct the false and insert the
missing intersection between the roads.
Label Layout is needed to make the map
usable. The graphic elements part are a
set of primary elements like road names
an secondary elements such as distances
between cross roads and direction arrows
within the map. With the arrangement the
position of the secondary graphics
elements is described so that they are in
the right order next to the primary
elements which they belong to. The
placement constraints are needed to find
regions in the map where to put the
graphic elements without occlusion.
For better orientation on the map the
Context Layout is responsible. Cross
street elements are placed for better
orientation where the user is on the map,
for example counting of streets he has
passed. Remarkable landmarks are also
important for a easy orientation, in this
case landmarks are big buildings, highway
signs, rivers ore mountains.
In order to enhance the usability of the
map and to complete the Line Drive
pipeline the Decoration is done as last
step. Because some roads are very short
after the Road Layout it is impossible to
place the road labels next to these roads.
To solve this problem some extensions are
made to have enough space to place the
road labels and to accentuate turning
points.
The rendering style defines the type of the
road, so that the driver easily can see
which type of road he actually uses. In the
last part of the whole layout step the
orientation arrow is set. In most cases the
arrow is set into one of the 4 edges and
point to the north
6
Results
The whole LineDrive algorithm is able to
make navigation a lot easier by drawing a
sketch
map
without
unnecessary
information and distraction. With the
implementation of this algorithm into
“MapBlast” there was an easy tool created
to plan a route.
7
Conclusion
LineDrive provides easy navigation without
any distraction. Yet, it is no navigational
system like it is known nowadays, because
it has no real-time capabilities like GPSsupport. If the driver leaves the route,
willing or unwilling, no additional information can be loaded to update the route
map. LineDrive is just a tool, which
produces an easy to read and easy to
handle route map from a particular starting
point to a certain destination.
Daniel Huffmann closed his obituary on
LineDrive like this: "I never used to draw
route maps by hand; I would simply write
verbal directions and bring an atlas.
Discovering LineDrive changed that,
though. Every long and unfamiliar trip
since then has started with me taking pen
to paper and sketching out a simple linear
cartogram to get me where I want to go."
8 Sources
[1] Agrawala, M., Stolte, C., „Rendering
Effective Route Maps: Improving
Usability
Through
Generalization“,
2001- 5-13
[2]
Huffman,
D.,
„Remembering
LineDrive“, 2011-3-8, http://something
aboutmaps.wordpress.com/2011/03/08/re
membering-linedrive, [2012-11-26]