ADDING METADATA TO MAPS AND STYLED LAYERS TO
IMPROVE MAP EFFICIENCY
B. Bucher, S. Mustière, L. Jolivet, J. Renard
IGN-COGIT, Saint Mandé, France
Introduction
Standard APIs to visualise geodata on information infrastructures, like OGC
MapContext (OGC 2005) or StyledLayer Document (OGC 2007), focus on specifying
the map spatial extent, size and styled layers. The selection of styled layers mostly relies
on portrayed features and on the layer acceptable resolutions. Theoretically, the
selection of a styled layer could in a near future also rely on the nature of portrayed
features based on semantic annotations of feature types in catalogues. But more criteria
need to be considered when designing a map, e.g. what relationships between features
should be visually rendered or what will be the ambient light. More generally,
cartographers point out the relevance of relying on a map requirements to design more
usable maps which include usable styles (Forrest 1999) (Chesneau et al. 2005)(Nivala et
al. 2007) (Jakobsson 2002) (Stanek et al. 2007)(Bucher et al. 2007).
There are two distinct issues addressed in this paper.
First issue is that defining fixed styles, e.g. for each INSPIRE layer, that will be used on
any map is a very challenging task –if not impossible-. Yet, on the fly definition of
adapted styles and feature portrayal is a costly process. A compromise is to define a
registry of different styles for the same layers in order to adapt to different ‘criteria’
regarding the final map.
Second issue is that many new map makers usually have no academic background in
cartography (Gartner and Peterson 2007). They may not always be capable of retrieving
relevant styled layers for their map in a registry based on the existing styled layers
description (feature types and styling rules); they need an abstract querying model. This
also holds when the map maker uses a graphical client to build his map from existing
layers flows.
In this paper, we introduce both an abstract map specification model and a registry of
predefined styled layers, focused on the adequate usage of colours in topographic maps.
We illustrate the relevance of the different elements of our model based on three
sources. The first one is the French Geoportail experience. The second one is the
usability study performed by (Nivala et al. 2007). They have evaluated the usability of
Web maps based on end user tests and on expert assessments. The third source is a
study where we have extrapolated large scale topographic maps keys from 15 European
countries to the French BDTOPO® data model and applied the adapted keys to the
same set of BDTOPO® data.
Figure 1. Maps obtained by extrapolating to the same IGN dataset the styles of topographic
maps from Austria, Norway and the Netherlands. Each map corresponds to a StyledLayersGroup
in our registry.
An abstract map specification model
A first item of our proposal is a formal model for map specification that can be used by
a novice map maker to specify the objectives of his map so that programs on the server
side can help him retrieve (or define) efficient styles for his map and evaluate his map
efficiency. This model is illustrated on Figure 2.
OBJECTIVES
Profile
age
nationality
gender
activity
Context
network
support
<readers
context>
Map
category
emotional impact
reference scales
area
Domain
nature :
internalrelationship :
Relationship
type :
FirstSight
CONTENT
Communication level
type :
order :
Reading1
Background
DRAWING
StyledLayer
Figure 2. Map Specification model.
In the following of this section, we explain the relevance of different criteria integrated
in this model.
One criterion is the relationships (association, dissociation, order) between features.
There exist relationships between coloured objects that are intuitively interpreted by the
reader into relationships between portrayed features (Bertin 1983). Similar hues convey
a relationship of close natures, variation in intensity conveys a order relationship
between thematic categories, and so on. Thus it is important to specify which
relationships are relevant and should be portrayed on the map so that colours are
selected and evaluated to render these relationships. (Nivala et al. 2007) have detected
usability issues for MapQuest maps which used a similar colour for shopping areas and
hospitals. With respect to this criterion, several styles for the same topographic layer are
necessary to adapt to the overlay of thematic layers: the map maker should select a
topographic background that does not use any colours too close to his layer colour. For
example, on the French Géoportail, unfortunate graphical relationships occur when
overlaying an avalanches layer over a topographic map because avalanches are
portrayed with the same color as hicking tracks on the topographic layer (see Figure 3).
Figure 3. Overlay of two styled layers on the ‘Géoportail’: IGN topographic map and an
avalanches layer.
Another criterion is the respect of colour conventions to facilitate the interpretation of
objects semantics: what colours are usually chosen to portray specific themes (water in
blue) or to render specific properties (danger in red). (Nivala et al. 2007) detected for
example usability issues related to the use of blue to portray motorway in MSN Maps
and Directions whereas blue semantically refers to rivers. These conventions are not all
fixed. They are sometimes specific to thematic domains, like the risk domain (Stanek et
al 2007), and sometimes specific to local culture. In our European legend test, people
(IGN employees) found it easier to read topographic maps with styles similar to IGN.
This is why user profiles have been added in our map specification model; to select the
relevant convention wrt user profiles and map domains.
Another criterion is the relative importance of features on the map. In the study on
European topographic legends, it is interesting to see how the resulting maps differ
regarding the relative importance attached to different feature types. Like (Kent 2009),
we believe this is an important interpretation of the landscape.
Other criteria, much studied in ubiquitous mapping, are the profiles of readers and the
expected reading conditions to read the map like the ambient light or the support
(Jacobsson 2002). These elements have been integrated in our map specification model.
A registry of predefined styles and styled layers associated to combination
evaluation procedures
A catalogue of predefined styled layers is under construction. This aims at assisting a
map maker in finding adequate styled layers for his map based on a query like like ‘a
topographic map for land planner engineers, with this specific featurecollection
portrayed with this green pictogramme’ (see Figure 5). The catalogue references
combinations of styles (FeatureStylesGroup) and combinations of styled layers
(StyledLayersGroup). Importantly, an aggregate should not be created and documented
automatically without specific evaluation mechanisms. The concept of
FeatureStylesGroup is useful to store map templates. We introduce the attribute ‘type of
area’ for FeatureStylesGroup because a symbolisation may or may not be adapted to a
given physical landscape.
StyleProcessing
Operation
effect
Same descriptors as
a map intentional
and functional levels
FeatureStylesGroup
category
emotional impact
reference scales
type of area
domains
relationships
communication level
user profile
context
StyledLayersGroup
emotional impact
area
domains
relationships
communication level
context
StyledLayer
FeatureStyle
Figure 4. Catalogue model.
FeatureCollection
Figure 5. Two different FeatureStylesGroup applied to the same Feature Collections: in the
second case, a user layer has been added.
Specific operations must be implemented on the server side to retrieve layers. For
example, if the map maker should use a user layer with fixed colours it is important to
retrieve a topographic background which colours are the furthest from the user colour
(illustrated Figure 5).
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