The 151 people completed the survey, in particular 113 (73%) male, 39 (25%) female respondents, and two participants who preferred not to communicate their gender. A greater part of the responses, 47 (31%) and 42 (27%), was received from persons aged 25–34 and 35–44 years old, respectively. The other respondents’ age groups were 45–54 years old, 26 (17%), 23 people over 55 (15%), and 15 participants aged 18–24 (10%); one person preferred not to indicate their age. Most of the people who completed the survey have a master’s (54/35%) or a doctoral (47/31%) degree, while the rest of the interviewed persons’ highest level of education is a bachelor’s degree (23/15%), a professional degree (11/7%), a high school degree or equivalent (14/9%), or less than a high school diploma (3 or 2%); two people preferred not to say. The respondents evaluated their experience with maps as follows: 83 (54%) of them create maps, 37 (24%) deal with maps on a daily basis, the other 28 (18%) use maps weekly, while 6 (4%) use maps rarely. These numbers show that the survey reached its target audience, but also gave the possibility to obtain feedback from non-cartographers. The respondents indicated in “%” their familiarity with relief shading, and on average, it amounts to 68%; 56 participants were 80%–100% familiar with relief shading (of whom 28 indicated 100%) and thus formed the experts group; 42 respondents indicated more than 50% and 23 less than 50%, including 9 people who were not familiar with relief shading at all.
Obtaining additional survey results as detailed qualitative comments allowed for explanations which characteristics or aspects respondents took as a basis for evaluation, why they made specific choice, what difficulties they experienced when answering the questions, and provided suggestions of what can be improved and, generally, ideas and observations.
3.2.1. Block Mountains
As may be seen from Figure 7
, almost the half of the respondents (47%) chose the clear sky model method as the most suitable for the depiction of the block mountains. Relief shading with NNW illumination was mainly considered rather suitable whereas texture shading rather not (32%) or least suitable (29%) for portraying the landform. Cluster shading received 44% of the answers as being rather suitable, while the MDOW method was considered to be rather inappropriate for this landform (29% for rather not suitable and 29% for least suitable). The most controversial method appeared to be the clear sky model with vertical exaggeration, since it scored high enough numbers in each of the categories: 31% believed it is actually the most suitable method, 18% rather suitable, 16% could not decide, 25% rather not suitable, and 10% the least suitable method for depicting this landform.
The numbers above largely correspond to more than 40 comments left to this question. Most of the respondents emphasized that the texture shading method gives a very flat impression and does not allow for recognizing the peak and height differences, although it reveals or highlights structures hidden in other images. It also contradicts to the aerial perspective effect, since its darkest parts on the shadowed slopes filled the feet of the mountain instead of their peaks. Besides, it looks soft enough to lose detail. Another likely unsuitable method for this landform is MDOW. This method gives the impression that the landscape is less steep than it seems in all of the other examples, it does not capture the overall impression of the hand-drawn version, has excessive detail in the lowest part of the slopes and lacks expressiveness at the peaks. Several respondents called this shading “plastic” or even looking fake; the others, on the contrary, noted that the higher level of detail was valuable and appealing to them, and assisted them in reading the terrain. The influence of vertical exaggeration applied to the digital elevation model before generating the hillshading can be fully assessed in the comments of the users. While some of them claimed that it is generally too dark, particularly in its northern valley, and there is not enough contrast between the slopes, at the same time it gives the most engaging and realistic impression for many participants and was recommended for depiction of larger relief forms. The NNW and cluster shading images delivered not only visually very similar results, but also similar comments: most of the participants distinguish the best grey-scale contrast leading to a better readability of larger forms and clear light shadow contrast that help to reveal more detail on shadowed slopes, but also note they are a bit too sharp compared to other examples. The main difference between the two is that cluster shading allows for better readability of the minor slopes, but on both images black spots in shadows hide information about relief, which is their major drawback compared to the first method. Finally, most respondents marked the clear sky model method as the best way for depicting the block mountains, as it provides the most balanced contrast, it is not overly detailed and also has a broader shadow and illumination area accentuating the larger forms. At the same time, several participants consider it looking a little too flat compared to the two previously discussed techniques.
The experts’ opinion is solid here, they likewise gave preference to the clear sky model method emphasizing that it has a full tonal range, good contrast without saturation, its shadows and illumination nicely define the pointy top of the Matterhorn, and it also has broader shadows and illumination that shows the entire ridge that the Matterhorn sits on. Several experts also appraised the cluster shading highly and recommended it on a par with the clear sky model or tended to prefer to add vertical exaggeration prior to applying the clear sky model, which brings more 3-dimensionality.
3.2.2. Folded Mountains
When choosing between the methods to depict folded mountains, the respondents gave more scattered answers (Figure 8
). For the folded mountains based on the presented images, the MDOW and texture shading methods were substantially considered as rather not (38% and 33%) or least suitable (23% and 33%, respectively). Nearly the half of the participants (48%) agreed that the cluster shading is a rather suitable method. A greater part of the respondents gave the preference to the clear sky model, saying that it is either the most (31%) or rather suitable (46%) method. In combination with the vertical exaggeration, the clear sky model gained 35% of all the answers for being the most suitable method to apply to this landform. Lastly, the NNW scored the third of all the votes (36%) to be a rather suitable method along with the both clear sky model methods.
After a closer look at the numerous comments of the participants, we can make the following conclusions. As in the case with block mountains, the MDOW method delivers generally a too noisy image with little details disturbing the whole relief shading and preventing the map readers from recognizing the main relief structures and forms and interpreting the relief as a whole. Cluster shading was generally commented upon in a rather positive way in that it has a nice contrast balance and is easy to read without changing the contrast, but it was also noted that larger forms look disintegrated. The clear sky model, both with and without vertical exaggeration, received the most positive feedback from the participants. Without vertical exaggeration, it provides the best contrast, makes it easier to identify the larger forms, and overall is less noisy than other examples. While with vertical exaggeration, despite too much contrast and dramatic effect, it attracted the respondents by its expressiveness and the strong sense of three-dimensionality, form and folding that it produces. Although the NNW illumination was considered rather suitable to apply to the folded mountains, it lacks the contrast and aerial perspective effect.
The expert opinions here vary, mainly between the sky model with and without vertical exaggeration. The clear sky model method was commented upon as the one that has a full tonal range and the right amount of white illumination and black shadows near the top of the highest ridges where it is needed most, whereas the vertical exaggeration conveys expressiveness and reveals most of the relief; at the same time, it exaggerates the heights and gives the impression of higher mountains, while many respondents like softer shadows for this type of relief. The texture shading method with regard to depiction of folded mountains shows too little contrast differences, thus preventing the users from understanding the heights, and better conveys the steepness of the slopes than the type of terrain. Cluster shading generates the darkest areas on shadowed slopes.
3.2.3. Mountains Formed by Erosion Processes
As in the two previous cases, prevailing number of the respondents answered that the clear sky model generates the best shading also of the lower mountains formed by erosion processes (Figure 9
). Texture shading and the MDOW method were considered to be unlikely suitable for this purpose. Cluster shading was overall regarded as favourable method for this type of the terrain, and a little less was the hillshading with NNW illumination and the clear sky model with vertical exaggeration, respectively. Although, the latter received the second highest number of answers as the most suitable technique.
Based on the comments of the participants, both clear sky model method and cluster shading provide good contrast allowing for grasping topography and recognition of larger forms. Increasing the vertical scale, according to most respondents, gives too rough an impression and makes the mountains look too exaggerated and fairly higher than in reality, although it emphasizes ridges and valleys well, which helps to read the terrain in an intuitive way. More even histogram tones produced by NNW illumination make a softer effect but still let the participants read the terrain easily. The terrain texture shading, as in the previous cases, is too light and not eloquent enough for differentiating the heights and relief forms, but is certainly suitable as a basemap. Finally, the MDOW method was claimed not to have the same level of detail as other examples, the aerial perspective effect is missing on it, and several respondents called it an aluminium foil due to its metallic look.
In relation to this landform, the opinion of the experts was not unanimous anymore. Each of the six methods was chosen as the most suitable by one or another expert. One of the critical issues mentioned was the relief inversion, which is present in all the methods shadings to some extent, except for the texture shading and the exaggerated clear sky model. As it is one of the worst drawbacks a shaded relief may have, the users may even prefer an exaggerated terrain over that suffering from relief inversion. The other part of the experts would rather use the texture shading with fewer deep shadows but remaining detail, so that they could easily complement it with other thematic data. Some of the experts believe that none of the shadings presented show the large relief forms or balanced contrast like the manual example.
With respect to drumlins (Figure 10
), equal parts of the respondents (each 30%) suggest that cluster shading and the clear sky model are the best two methods to portray the drumlins. The rest of the four techniques each yielded less than 10% of the answers, out of them the participants preferred the standard hillshading with NE illumination over the other three methods.
In their comments, the participants explained, that none of the suggested methods could perfectly cope with the task to visualize the flow direction of the glacier, on the one hand, and to keep the individual shape of the drumlins, on the other hand. The first two methods make the best impression, since they show the relief of the terrain, the direction of the slopes, and preserve the rounded shape of the drumlins.
The expert group delivered miscellaneous comments with regard to depiction of drumlins. Based on their common opinion, the clear sky model is the most appropriate method to depict drumlins, as it produces the most balanced shading, and also the rounded shape of the drumlins better resembles their natural look like on the Google Earth image (although not the manual relief shading). The standard hillshading with the NE illumination provides a nice pattern, but its 3D effect is subtle. Several respondents recommended to either apply multiple light sources or NE illumination when generating the shading using the clear sky model, in order to reach the best visual effect. Local hypsometric tints make drumlins look too narrow and linear. The MDOW could be an appropriate technique for drumlins, if it would not bring the excessive detail in flat areas, that disrupt the overall pattern and might also distract the map user. Generally, on most of the shadings (except the standard hillshading) the grey value in flat areas is too dark, and without adjustment, none of these images would be directly usable.
The most suitable method for plateaus appears to be a difficult choice for most of the respondents (Figure 11
). There is no unanimous opinion among both non-cartographers and experts. With a slight superiority, clear sky model with and without vertical exaggeration and standard hillshading with NNW illumination make a better impression of the relief of the plateaus.
Analysis of the comments gives a better idea of respondents’ reasoning. Those who gave a preference to the clear sky model claimed that its stronger shadows and flat upper areas draw out the landforms in the best way, that this method provides the best interplay of terrain elements, and brings a natural look to the terrain. The same method in combination with altering the vertical scale of the terrain looks more pronounced than even the hand-drawn version, is very clear with regard to overall terrain, and has a stronger three-dimensional effect, as happens when relief becomes deliberately exaggerated. On the other hand, it is certainly extreme and dramatic, as noted in every second comment. Clear sky model and cluster shading images reportedly look too similar to tell them apart which is, first, interesting and, second, is only the case with the plateaus. Apparently, for this reason they were evaluated in a similar way. Texture shading shows the pattern of a plateau well but looks too flat to the great part of the participants, and the MDOW method starts to look like a foil once again.
Several experts noticed that the manual relief shown here does a poor job at depicting the plateaus, making the top parts of the plateaus rounded instead of flat. Thereby, most analytical shadings here deliver better result than the manual one. A mix of the top part with the vertical exaggeration with the lighter incised part as that one provided by the standard hillshading, was suggested as a possible improvement.
3.2.6. V-Shaped Valleys
Despite its exaggerated contrast and overall look, the 40% of the respondents found the clear sky model shading with vertical exaggeration generally more appealing for V-shaped valleys compared to the other examples (Figure 12
). Without increasing the vertical scale, the clear sky model method produces the best shading, according to a quarter of the respondents. Very close (21%) is texture shading, which this time proved to deliver proper shading for this type of terrain. Both cluster shading and standard hillshading with NNW illumination look least pronounced with respect to V-shaped valleys.
According to the respondents’ comments, the relief inversion appeared to be a big problem present at this terrain again, including the manual relief. To some participants, the manual example looked unusual and sophisticated as a reference. The MDOW shading once again looks overly detailed to many and has a metallic effect. The main deficiency of the standard hillshading here is that, despite the adjusted NNW illumination, it reportedly lacks contrast and thus clarity when distinguishing the larger forms. In contrast, cluster shading proved to have better emphasized the ridges. Texture shading brings more contrast and darker tones in the valleys, and as a result prevents the relief from inversion and accentuates the heights. As for the clear sky model alone, the respondents agree that the generated relief has appropriate balance in shading and more accentuated ridges, but vertical scale changes make it possible to better emphasize also slopes as a part of larger relief forms.
The experts could not help but notice that excessive dimming in the valleys, brought by the increased vertical scale, contradicts the aerial perspective effect on the shadowed slopes, where the darkest tones should appear at the highest parts next to the ridges and not down in the valleys. Even though the darker lowland tones prevent the shading from relief inversion, it would be hard to use such a high contrast relief on a map, as noted multiple times. Larger forms are not well developed in all the examples, and none of the shadings clearly shows the bright and the dark slopes of the valley. But a combination of more pronounced ridges, generated by a clear sky model or cluster shading, with the well-distinguished large slopes, which is possible due to increasing the vertical scale, would bring a substantial improvement in this case.
3.2.7. U-Shaped Valleys
One third of the respondents preferred clear sky model with the south illumination, i.e., light direction perpendicular to the direction of the valley, for the depiction of U-shaped valleys (Figure 13
). The same method combined with the vertical exaggeration, the MDOW and the clear sky model with the standard NW illumination received each about the same 20% of the votes, while texture and cluster shading do not look that favourable for portraying U-shaped valleys.
Based on the respondents’ comments, the south illumination brings an appealing look of the U-shaped valley, expressed in well-balanced grey tones, in the intuitive recognition of the relief forms, and in a characteristic roundness of the valley, which is peculiar to this landform. The NW illumination works also well for this type of valleys and properly accentuates the steep sides, despite the black stripe down the slope stretching parallel to the valley floor. The MDOW method reveals too much detail, while texture shading does not look very eloquent in achromatic tones and suits better for colour relief shading. Cluster shading does not capture the flat floor of the valley very well and has too dark a slope, which contributes to the fragmentation of the image. Finally, changes in vertical scale provide stronger contrast and represent a steeper and narrower valley floor, which is misleading with regard to a U-shape and give more impression of a V-shape. It also raises the same issue with the aerial perspective effect, as in case with V-shaped valleys.
Another example showing that the hand-drawn relief is not always superior to digital relief is the U-valley floor that appears wide in all the examples, except in the hand-drawn one, as aptly noticed by the experts.
3.2.8. Alluvial Fans
One third of the respondents considered the hillshading with the light direction from the west, i.e., perpendicular to the alluvial fan slope, the most successful solution to accentuate alluvial fans (Figure 14
). The other significant part of the participants (18%) decided that also the MDOW method performs well in this case. The rest of the methods were not very convincing, and the respondents could not explicitly decide between them.
There are not many comments from laypersons, except that several people noted that none of the examples is particularly successful in depicting alluvial fans. The experts generally shared the same opinion. They mentioned that it is difficult to only look at these little geomorphological forms without considering the rest of the terrain, and that showing them separately would require a hillshading with terrain segmentation. Relief inversion was also the case with alluvial fans. The experts commented on differences between the methods as follows. The MDOW method provides the most fan detail and variation in the features in the valley floor. Vertical exaggeration in the clear sky model method makes it difficult to distinguish the fan from the edge of the mountains due to its darkness. The texture shading looks too flat, while both the valley floor variation and the hillsides are most evident in the hillshading with the western illumination, clear sky model, and cluster shading. The possible improvements offered are post-processing of alluvial fans, changing a data source to light detection and ranging (LIDAR) data instead of a DEM, and adjusting the light direction so that it does not coincide with the direction of the fans slopes.
More than 40% of the respondents (Figure 15
) chose aspect shading as the most suitable method to apply to glaciers. A clear sky model, MDOW and cluster shading received overall a positive feedback, too, while texture shading and local hypsometric tints techniques most participants found to be least suitable for this purpose.
Despite an impressive level of detail and preservation of the flow marks on the surface, the aspect shading was also commented on as a very sharp, exaggerated method depicting a specific state of a glacier, as it is usually always in motion. A clear sky model and cluster shading bring out less detail on the surface of the glaciers’ surface, thus are not overloaded. Concerning the MDOW method, the participants commented that it shows the flow of glaciers nicely. Texture shading reveals a mountainous structure and glaciers very nicely, but the difference between snowy patches and snow-free area is not always clear nor correctly depicted. The glacier texture produced by local hypsometric tints, as well as by cluster and texture shadings, almost reminds one of a water surface instead of an ice surface.
The experts likewise chose mainly between the first four methods described above. The clear sky model depicts nicely both mountains and ice, aspect shading provides rich details on the glacier surface but at the same time gives an impression that mountain and glaciers are smoothed into each other. The MDOW is the method to go with for glacier detail, and cluster shading is here a compromise between the mountain and glacier detail. In the texture shading, mountain peaks look snowy and the glaciers look smooth, while the local hypsometric tints shading looks flat to the most respondents, even though it does show striations in the glacier. Several experts concluded that the ice texture does not have to stand out, but should look different to the rest of the terrain, and there is room for improvement with respect to larger relief forms to make them more visible.