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Noot
De heer F.A.N. Declercq is vorig jaar aan de Katholieke Universiteit
te Leuven gepromoveerd. Dit artikel is naar aanleiding daarvan ge-
schreven. De oorspronkelijke titel van de (niet uitgegeven) dissertatie
luidt Computergestuurde visualisatie van kaartinformatie: interpolatie,
klassenindeling, symboolgebruik. Prof. F.L.M.L.J. Depuydt was de pro-
motor van het onderzoek.
Summary
F.A.N. Declercq F.L.M.L.J. Depuydt - More efficient Classi
fication and colour use in choropleth maps
Keywords: visualisation, thematic cartography, research
The efficiency by which map users can extract quantitative in-
formation from choropleth maps is assessed. By means of a map
use test, the influence of the type of colour scheme (area fill),
the number of classes and the rounding of the class limits are
investigated. Results show that the use ofonly gray tones prohi-
bits the reading of map information compared to the use of
schemes containing more contrasting variations of hatch pat
tern or colour. Choropleth maps with fewer than 6 classes are
not suited to display local map information: the use ofy to 11
classes is hereby recommended. To accomplish a perceptually ef
ficient presentation of regional variations the use of9 to 11 clas
ses becomes too complex, whereas again the 7 class maps yield
optimal scores. Map users capture map information more pre-
cisely and faster if class limits are rounded to one digit instead
of two or three digits afier the decimalpoint.
Resume
F.A.N. Declercq dr F.L.M.L.J. Depuydt - Classification et
emploi de couleurs plus efficaces pour des cartes choropletes
Mots-cles: visualisation, cartographie thematique, recherche
L'ejficacite avec laquelle les utilisateurs de cartes choroplethes
peuvent extraire de l'information quantitative et ordonnee est
examinee. Partant d'un test d'emploi des cartes, Tinfluence du
type de variable retinienne (implantation zonale), du nombre
de classes et de la fagon d'arrondir les bornes de classes est eta-
bli. Les resultats montrent que l'usage d'une Variation de va-
leurs de gris donne une lisibilite profondement inferieure com-
pare aux progressions contenant des variations de couleurs ou
de semis. Des choroplethes constituant de moins de 6 classes ne
sont pas propre pour lire des informations locales dans la carte:
l'usage de 7 11 classes est recommende pour ceci. Pour accom-
plir une repartition en struetures regionales par une maniere
efficace, l'emploi de 9 11 classes devient trop complex, tandis
que les cartes 7 classes nouveau obtiennent un score opti
mal. L'extraction d'information se fizit plus precisement et plus
vite si les bornes de classes sont arrondies jusqu'ä un chiffre au
lieu de deux ou trois chiffres.
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