Geography Reference
In-Depth Information
Requirements for the Color Scheme
We recommend strongly to define requirements before the development of a
scheme. These should consider the color design guidelines specified in section
“Color Design Guidelines” and should give an indication of the criteria for decision
support (section “Criteria for Decision Support”). In our use case described herein,
prerequisites were the class range and the number of classes determined by EU and
national law.
Alberts and Alferez (
2001
) suggest the following considerations for the
END-scheme: The scheme should cover a wide range of noise bands from 40 to
more than 80 dB(A); noise bands below 50 dB should be in green colors; the bands
over 65 dB(A) in red; it should be suitable for different noise indicators like L
day
,
L
evening
and L
max
and noise bands of 5 or 10 dB; colors should differ sufficiently;
rather topographic objects should be transparent instead of noise bands; color codes
such as HEX and RGB should be provided.
We agree with the considerations above, but we add more detailed requirements
based on our color design guidelines. Thus the colors of the scheme should be:
Distinguishable for people with CVD as well as when used for areas of different
size, in different scales and a variety of screens;
consistent and therefore facilitate a matching of colors used in the map with
colors of the map legend;
logically assignable to the characteristics of the noise data; i.e., that presented
noise levels should not be under- or overestimated, hotspots and silent areas
should be determined by the users without referring to the map legend and colors
should facilitate an association with the categories of noise levels.
According to our criteria for decision making the priorities are therefore to
highlight a critical value (1.b.i) and to induce a three-dimensional effect (1.b.ii).
The level of abstraction is 2.b., hence the colors should be in association with the
annoyance levels.
Designing a Color Scheme
The design was carried out iteratively in three steps. Several empirical user studies
have been conducted throughout the development process. The first version of the
scheme was designed according to cartographic standards as a sequential scheme
with two hue-steps (yellow/orange, orange/red), but it did not satisfy noise experts
because the different shades could not be distinguished in cases where ten classes
were visualized, which is done frequently in Germany. After a discussion with
experts from the
German Standardization Organization
requirements were defined
not only with a focus on cartographic rules but also with focus on the specific use
case and practical requirements. In the second design, therefore, more hue-steps
