By Mamata Akella, Esri Design Cartographer, and Kenneth Field, Esri Research Cartographer
In the first of our Canvas Maps blogs, Esri Canvas Maps Part I, we explained the initiative and philosophy behind the new suite of Canvas Maps being developed by Esri. They are a new style of basemap designed with neutral colors, minimal features and detail that allow you to map many of your operational overlays more effectively.
In this second part, we suggest some best practices to get the most out of the first of the Canvas Maps to be released, the Light Gray Canvas Map, and illustrate how it can be used effectively. The Light Gray Canvas Map works particularly well in combination with operational overlays that contain point and line features. By design, it provides users with a way of improving a number of key cartographic objectives such as developing a sound figure-ground relationship and hierarchical organization in your map.As with all basemap services, the Light Gray Canvas Map is not suitable for all mapping purposes so we also offer some tips on avoiding some pitfalls and how to use operational overlays to offset some of the limitations to improve your overall map design.
The Light Gray Canvas Map is available here on ArcGIS.com. It is available as a basemap via the dropdown in ArcGIS for Desktop 10 and will be added to the basemaps available in the ArcGIS.com map viewer and ArcGIS Explorer Online. Let’s take a look at some examples and see how we can use the Light Gray basemap effectively.
Building a better graphical structure
Hierarchical organization relates to the level of visual importance you assign to information in your map through the design. As the map maker, it is up to you to decide how information is organized based on the message you want to communicate. A good hierarchy is achieved when the map user sees features in a way that relates to the relative importance of the various map components. A good figure-ground relationship is established when the map’s main theme is symbolized to stand out and the contextual background designed to recede. Using the Light Gray Canvas Map, you can build effective hierarchical organization effectively since a greater range of symbol options are available for you to use in your operational overlays. In other words, the basemap uses a narrow range of symbols and the minimal structure leaves you with a wider palette of design to apply to the important part of the map: your operational overlays. A good figure-ground relationship is established by using saturation to good effect when symbolizing operational overlays. Because the Light Gray Canvas Map uses subtle colors it’s design allows it to recede to the background and provide the ‘ground’ to the ‘figure’ of your operational overlay.
Since the Light Gray Canvas Map uses a predominantly monochromatic grayscale color scheme for the basemap, modifying the saturation of a color to either highlight or push back a mapped feature works well for symbolizing the operational overlay. In essence, the lower the saturation value, the more gray is introduced into a color. Therefore, if you want to give a subtle appearance to your operational overlay, you would use colors that have low saturation (figure 1). On the other hand, if you really want your thematic information to ‘pop’, you would use colors that have a higher saturation (figure 2).
Figure 1. Using low saturation in operational overlay symbology.
Figure 2. Using highly saturated colors in operational overlay symbology
With this fundamental concept, we can begin to build upon the Canvas Map in numerous ways. Depending on your message, you can choose an appropriate method to symbolize your data. The Light Gray Canvas Map allows you a richer set of design possibilities since you are not competing with numerous colors and the wider symbol palettes contained in other basemaps. Figures 1 and 2 also illustrate the effectiveness of using Light gray Canvas Map as a background for point-based thematic data, in this case proportional symbols.
Adding emphasis to basemap components
The basemap design is deliberately non-heirarchical and no one feature is given importance over another. In other words, the visual layering between map features is limited so the map can serve well as a base layer. As we explained in the first Canvas Map blog, we excluded information by design on Canvas Maps – but what if you want to add more reference information to give more contextual information in support of your operational overlay? In this case you would choose to symbolize additional reference features using colors that are low in saturation so they sit naturally and unobtrusively in the background, but which also emphasize them subtely. This technique adds value to the basemap to emphasize certain features but remains non-figural. Additonal operational overlays can still be added to create the finished map.
To illustrate this concept, figure 3 provides an example of adding an operational overlay showing major highways in Oregon using colors low in saturation. In doing so, the highways sits well on the basemap and remain unobtrusive. The highway shield labels are also designed to sit unobtrusively using low saturation.
Figure 3. Additional reference information can be added to augment basemap detail
Symbolizing thematic overlays
Now let’s take a look at another situation where we would like to symbolize thematic data so that it comes to the foreground of the map (i.e. it becomes figural). We can see how this might be developed by building on top of the Oregon roads example in figure 3. This approach works particularly well for point and line datasets and, by inference, for thematic maps where we are looking at statistical data or we want to clearly illustrate patterns such as clusters through the map.
Say we want to map the locations of man-made fire incidents in the state of Oregon over a 15 year time period. Symbolizing the highways to augment the basemap provides a useful context to enable us to better understand the pattern of fire incidents. For the fire locations themselves, we’ll symbolize them using a highly saturated orange. Figure 4 illustrates the result of this approach and shows the fire incidents as strong figures with the highways providing a good context over the underlying basemap.
Figure 4. Location of fire incidents are symbolized with a highly saturated orange
Figure 5 shows the city origin of attendees to this year’s Esri International User Conference from the contiguous 48 United States. We can infer, based on the symbol size, how many people are coming from each city and using a highly saturated single color for the symbols on the Light Gray Canvas Map works well to make the data stand out.
Figure 5. Attendance at the 2011 Esri User Conference
Because of the extended color palette we can now use, given the use of the Light Gray basemap, we can apply different saturations to the symbology to accentuate key dimensions in the data. In figure 6, we’ve highlighted the locations where there are more than 100 people attending the User Conference from a particular city. To do this, we symbolized all classes with less than 100 attendees in a color with relatively low saturation and everything greater than 100 in a color with a higher saturation. This approach to symbolization would not be possible on a basemap that contained a wider color palette without compromising the visibility and legibility of the symbols themselves.
Figure 6. Attendance at the 2011 Esri User Conference with modified symbology
The case of polygonal operational overlays
In the previous two examples we looked at how point and line overlays can work well with the Light Gray Canvas Map. The Light Gray Canvas Map was designed to specifically support point and line data. With any basemap, both continuous and non-continuous polygon overlays are also able to be used as operational overlays but where polygonal data is overlaid the basemap is obscured. This has the impact of removing from sight not only the basemap detail but the reference information (country and city labels). In many circumstances a better basemap to use would be the Terrain with Labels basemap since the labels will sit above the operational overlay with polygonal data sandwiched between.
To avoid obscuring too much basemap detail when using polygon data we can use transparency on the operational overlay to ensure that some basemap detail is seen. However, it remains obscured to an extent and given the area of most interest in the map will have contextual detail partially obscured (with the surrounding basemap visible) this is less than optimal. It does not provide a satisfactory solution for someone using the map to understand the data in the area or theme of interest. What happens when we add transparency is we are decreasing the amount of color by introducing more gray. Given that the Light Gray Canvas Map uses various shades of gray for the design of the basemap, when transparency is applied to polygonal overlays; gray will be introduced which dulls the colors, although we can offset this to some extent using highly saturated colors.
A more effective way around this issue (for use on any basemap) is to use polygon outlines or pattern fills instead of color to symbolize the data. Details for this technique are in our previous blog Designing Operational Overlays for the ArcMap and ArcGIS Online basemaps. Alternatively, in addition to using transparency, we could add other operational overlays to offset the obscured basemap detail. Figure 7 illustrates how transparency (50%) can be applied to a polygonal dataset symbolized with highly saturated colors and, additionally, how obscured basemap detail (country boundaries and labels) can be added as additional operational overlays using colors that complement the contextual basemap. This has the effect of adding back in the lost basemap detail to provide map users with a suitable set of contextual detail. This same approach can be successfully applied to the use of the Light Gray Canvas Map as a basemap for choropleth maps to provide contextual detail to support interpretation.
Figure 7. Using transparency and additional operational overlays to offset the polygonal overlay problem.
In this blog we’ve explored some ways in which the Light Gray Canvas Map can support effective data display. We’ve illustrated how it can be successfully used for point and line data and how, with some adaptation, we can design a reasonable solution for the display of polygonal data. Check out the public group Samples that use light gray canvas basemap in ArcGIS.com where we’ve shared some examples of the use of the Light Gray Canvas Map to help inspire you to see the possibilities of displaying your data using this basemap. We will refine the examples over time and please let us know if you have a great example to share!