Bernhard Jenny

Cultural Heritage: Studying cartographic heritage: Analysis and visualization of geometric distortions

Old maps are increasingly used as a source for historical research. This is a consequence of the increased availability of old maps in digital form, of the emergence of user-friendly Geographical Information Systems, and of a heightened awareness of the unique information stored in old maps. As with every source for historical studies, when old maps are georeferenced and information is extracted for historical research, the accuracy and reliability of the geometric and semantic information must be assessed. In this paper, a method based on a series of geometric transformations is presented, which transforms control points of a modern reference map to the coordinate system of an old map. Based on these transformed points, the planimetric and geodetic accuracy of the old map can be computationally analyzed and various visualizations of space deformation can be generated. The results are graphical representations of map distortion, such as distortion grids or displacement vectors, as well as statistical and geodetic measures describing the map geometry (e.g., map scale, rotation angle, and map projection). The visualizations help to assess the geometric accuracy of historical geographical information before using the data for geo-historical studies. The visualizations can also provide valuable information to the map historian about the history of a particular map and its creation.

Adaptive Composite Map Projections

All major web mapping services use the web Mercator projection. This is a poor choice for maps of the entire globe or areas of the size of continents or larger countries because the Mercator projection shows medium and higher latitudes with extreme areal distortion and provides an erroneous impression of distances and relative areas. The web Mercator projection is also not able to show the entire globe, as polar latitudes cannot be mapped. When selecting an alternative projection for information visualization, rivaling factors have to be taken into account, such as map scale, the geographic area shown, the maps height-to-width ratio, and the type of cartographic visualization. It is impossible for a single map projection to meet the requirements for all these factors. The proposed composite map projection combines several projections that are recommended in cartographic literature and seamlessly morphs map space as the user changes map scale or the geographic region displayed. The composite projection adapts the maps geometry to scale, to the maps height-to-width ratio, and to the central latitude of the displayed area by replacing projections and adjusting their parameters. The composite projection shows the entire globe including poles; it portrays continents or larger countries with less distortion (optionally without areal distortion); and it can morph to the web Mercator projection for maps showing small regions.

Color Design for the Color Vision Impaired

Eight percent of men are affected by color vision impairment – they have difficulties distinguishing between colors and thus confuse certain colors that the majority of people see readily. Designers of maps and information graphics cannot disregard the needs of this relatively large group of media consumers. This article discusses the most common forms of color vision impairment, and introduces Color Oracle, a new software tool that assists the designer in verifying color schemes. Color Oracle filters maps and graphics in real-time and efficiently integrates with existing digital workflows. The paper also discusses color combinations and alternative visual variables for map symbology that those with color vision impairments can distinguish unambiguously. The presented techniques help the cartographer produce maps that are easy to read for those with color vision impairments and can still look good for those with normal color vision.

Visualizing the Planimetric Accuracy of Historical Maps with MapAnalyst

MapAnalyst is a new software application for the visualization and study of the planimetric accuracy of old maps. It illustrates local map distortion by generating distortion grids, displacement vectors, and new isolines of scale and rotation. MapAnalyst additionally computes the old maps scale and rotation, as well as statistical indicators summarizing the maps geometric accuracy. It offers a user-friendly interface and is freely available for all major computer platforms at . Map historians are invited to use MapAnalyst, and are encouraged to consult and improve the free Java source-code. This article describes the steps leading to visualizations of a maps planimetric accuracy. It provides basic algorithmic information that is necessary for the understanding and correct interpretation of displacement vectors and distortion grids. It also introduces isolines of equal scale and rotation, a new type of accuracy visualization. The last section interprets sample visualizations for an eighteenth century map.

An Interactive Approach to Analytical Relief Shading

The software currently available for analytical relief shading does not generally permit local adaptations of the light direction, the simulation of aerial perspective, and other necessary techniques developed for manual relief shading. To remedy this deficiency, a program for computer-assisted relief shading has been developed that allows users to locally adapt shading characteristics, permitting seamless interactive control over the entire process. The grey values of the image are determined by a combination of aspect-based shading for steep regions, diffuse reflection for lowlands, and a bright grey tone for flat areas. Furthermore, an algorithm for the simulation of aerial perspective is presented. Tests with the program have shown that, with minimal investment of time, the quality of analytically produced shaded relief can be improved significantly. Using the proposed techniques and software presented herein, experienced cartographers can transfer their manual relief-shading knowledge and experience ...

Flex Projector–Interactive Software for Designing World Map Projections

Flex Projector is a free, open-source, and cross-platform software application that allows cartographers to interactively design custom projections for small-scale world maps. It specializes in cylindrical, and pseudocylindrical projections, as well as polyconical projections with curved parallels. Giving meridians non-uniform spacing is an option for all classes of projections. The interface of Flex Projector enables cartographers to shape the projection graticule, and provides visual and numerical feedback to judge its distortion properties. The intended users of Flex Projector are those without specialized mathematical expertise, including practicing mapmakers and cartography students. The pages that follow discuss why the authors developed Flex Projector, give an overview of its features, and introduce two new map projections created by the authors with this new software: the A4 and the Natural Earth projection.

Swiss-Style Colour Relief Shading Modulated by Elevationand by Exposure to Illumination

Abstract Maps with coloured relief shading, modulated by elevation and by exposure to illumination, present topography in a particularly vivid and descriptive manner. Carefully modulated illumination and shading shown in continuous colour tones simulate the third dimension of topography, helping map-readers to conceive more easily the terrains important landforms. Since the end of the 19th century, cartographers have developed a wide variety of colour schemes. The first part of this paper illustrates the graphical and technical developments of the past, leading to Swiss-style coloured relief shading; the second part presents a new computer-based method for colourizing grey-shaded relief inspired by classic colour schemes. The method uses a colour look-up table and a digital elevation model. The colour look-up table has colours for all combinations of initial grey values and terrain elevations. It is constructed from interactively placed colour reference points.

Map design for the Internet

To successfully transmit spatial information, maps must be well-designed. There exists a canon of design guidelines for paper maps, but a concise compilation of guidelines for the design of web maps is currently not available. This chapter contributes to this need by providing recommendations and guidelines specific to the design of web maps. Topics include the choice of a viewing technology; the influence of limited screen resolution and anti-aliasing; minimum dimensions and distances for map features; the generalization of information density and geometry; problems of screen typography; color rendition and; the design of user-friendly navigation tools. Some of these guidelines are based on the authors’ mapping experiences, while others were deducted from the observation of Internet user behavior or compiled from selected sources.

Lightweight Relief Shearing for Enhanced Terrain Perception on Interactive Maps

We explore interactive relief shearing, a set of non-intrusive, direct manipulation interactions that expose depth and shape information in terrain maps using ephemeral animations. Reading and interpreting topography and relief on terrain maps is an important aspect of map use, but extracting depth information from 2D maps is notoriously difficult. Modern mapping software attempts to alleviate this limitation by presenting digital terrain using 3D views. However, 3D views introduce occlusion, complicate distance estimations, and typically require more complex interactions. In contrast, our approach reveals depth information via shearing animations on 2D maps, and can be paired with existing interactions such as pan and zoom. We examine explicit, integrated, and hybrid interactions for triggering relief shearing and present a version that uses device tilt to control depth effects. Our evaluation shows that these interactive techniques improve depth perception when compared to standard 2D and perspective views.

User preferences for world map projections

Many small-scale map projections exist, and they have different shapes and distortion characteristics. World map projections are mainly chosen based on their distortion properties and the personal preferences of cartographers. Very little is known about the map projection preferences of map-readers; only two studies have addressed this question so far. This article presents a user study among map-readers and trained cartographers that tests their preferences for world map projections. The paired comparison test of nine commonly used map projections reveals that the map-readers in our study prefer the Robinson and Plate Carrée projections, followed by the Winkel Tripel, Eckert IV, and Mollweide projections. The Mercator and Wagner VII projections come in sixth and seventh place, and the least preferred are two interrupted projections, the interrupted Mollweide and the interrupted Goode Homolosine. Separate binominal tests indicate that map-readers involved in our study seem to like projections with straight rather than curved parallels and meridians with elliptical rather than sinusoidal shapes. Our results indicate that map-readers prefer projections that represent poles as lines to projections that show poles as protruding edges, but there is no clear preference for pole lines in general. The trained cartographers involved in this study have similar preferences, but they prefer pole lines to represent the poles, and they select the Plate Carrée and Mercator projections less frequently than the other participants.