DESIGN AND PRODUCTION TIPS

This last section provides design and production tips for making natural-color maps and managing land cover data. Because of space limitations and the ever-changing nature of software, the intent of Photoshop tips described here is to give you design ideas and point you in the right procedural direction. The downloads area for this article contains additional resources related to the discussed tips. Prior experience with Adobe Photoshop is helpful. And given the large files involved, so too is a graphics workstation with large amounts of physical RAM, scratch disk space, and file storage.

Figure 17. Shaded relief merged with a natural-color base made from MODIS VCF data.


Tip 1: Combining shaded relief and land cover data

Shaded relief is an essential component on all natural-color maps (Figure 17). However, the textures in shaded relief and those found in land cover, if clumsily combined, have the potential to become heavy and messy. The following will help you use shaded relief more effectively with land cover data: 

• Show shaded relief and land cover with roughly equal emphasis. Despite the considerable effort that goes into transforming raw land cover data into a natural-color base, for the greater graphical good, do not to print these colors too boldly. The same rule applies to shaded relief. The relative visual prominence of shaded relief and land cover varies on a map depending on viewing distance. Up close the shaded relief appears more dominant as a dimensional texture. By comparison, when viewed from farther away land cover colors on the map become the more noticeable feature, appearing as broad generalized zones.
  
  
• Generalize shaded relief at reduced scales. Although land cover colors reduce to smaller sizes with no visible harm, shaded relief is not as elastic. Excessive topographic detail at small map scales only pollutes the background land-cover colors and detracts from our understanding of major topographic structures. Repurposing a natural-color map from, for instance, wall map size to textbook size requires replacing the shaded relief with a more generalized version. As a general rule the resolution of a DEM used to generate shaded relief should be equal to or less than that of the land cover. For example, if a land cover image is 10,000 pixels wide, the DEM used to generate the shaded relief might be 7,000 pixels wide. The resulting shaded relief is then upsampled (or rendered) to 10,000 pixels wide for final compositing with the land cover. The need for generalized shaded relief applies to all maps and not just those with natural colors.
  
  
• Remove shaded relief tones from flat areas. A typical shaded relief contains tonal values of 10 to 20 percent density in flat lowland areas. They serve as a neutral base upon which other topographic features, modeled by light and shadows, project upward or downward in a three-dimensional manner. While tones in flat areas are desirable for stand-alone shaded relief, the overall image becomes too dark when merged with land cover colors. A cleaner and brighter alternative is to let the land cover colors themselves do double duty as a base tone for the shaded relief. To do this use Curves (Image/Adjustments/Curves) or Levels (Image/Adjustments/Levels) to clip the tonal range of the shaded relief just enough to remove tones from the flat areas. This procedure works best with a shaded relief possessing a full tonal range including fine detail in the brightest highlighted slopes and densest shadowed slopes. Be careful not to remove too much tone, or the shaded relief will lack body and appear spindly. Using the Eyedropper tool and the Info palette permits the removal of tones with numerical precision.
  
  
• Show illumination. The illuminated slopes on a shaded relief are almost as important as shadowed slopes. They enhance the apparent three dimensionality of a shaded relief, giving it an embossed look and also lightening the image. To add supplemental illumination to a shaded relief, first create a Hue/Saturation adjustment layer (Layer/New Adjustment Layer/Hue/Saturation). Next, copy and paste the grayscale shaded relief into the adjustment layer’s layer mask. Then, in the layer mask, use Curves to choke the shaded relief tonal range so that all areas except illuminated slopes are black. For the final step double click on the adjustment layer icon to open the Hue/Saturation dialog and move the Lightness slider to the right until the illuminated slopes look appropriately bright. In Figure 16, the third layer from the top shows an illumination adjustment layer in Photoshop. A low-resolution version of this file is available on the website of this paper for you to download and examine.
  
  The adjustment layer technique also works well for displaying shaded relief shadows. The advantage is that the darkening preserves the varying colors below. For example, forest green becomes a darker green, desert beige becomes a darker beige, and so forth. The final result is a natural-color map with more pure natural colors. Creating shadows with a Hue/Saturation adjustment layer is similar to the illumination technique described above. But this time invert the shaded relief (shadowed slopes should be lightest) and move the Lightness slider to the left (start with settings between –55 and –30).

Tip 2: Legend design

Despite Shelton’s misgivings about their usefulness, legends do play an important role even on well-designed maps. Readers expect to find legends on maps, and cartographers are partial to displaying them. If a legend is a little redundant, that is a lesser problem than having no legend and uniformed map readers. Having said that, the design of legends on natural-color maps is worthy of reexamination. The traditional map legend explains natural colors with small, rectangular color filled boxes arranged neatly in a row and separated from one another. Typically a black casing line bounds these boxes. Such a portrayal disassociates the legend colors from one another and, of greater concern, from their counterparts on the map. If the map uses shaded relief and the legend does not, the communication disconnect is even greater.

Figure 18. (1-4) Variants of the traditional legend. (5) A natural legend. Legend portrayal becomes less abstract and more cartographically realistic from left to right.


To improve the design of traditional legends on natural-color maps, consider doing the following: remove the black casing lines, place the colored boxes in a contiguous row, include shaded relief, and, perhaps, blend the colors (Figure 18, examples 1-4).  The idea is for the legend to mimic colors on the map as closely as possible while still maintaining order. For another step toward this goal think about using a natural legend (Figure 18, example 5). Placing legend labels on an icon of the map itself communicates the meaning of colors directly and unambiguously to readers. Compared to traditional legends, the disadvantages of natural legends are that they require more space and are less tidy.


Tip 3: Mapping urban extents

Besides the making of natural-color maps, land cover data is a useful product for mapping urban areas as a stand-alone category on general maps. Isolating urban areas from the other categories in NLCD (and other categorical land cover data) is simple to do with the Magic Wand tool. Hint: set the tolerance to zero and do not choose the antialiasing and contiguous options. Having selected the urban areas, invert the selection (Selection/Inverse) and fill all of the other land cover categories with white. The image should now look something like Figure 19 (upper left). The next potential issue is one of generalization. Because the urban categories in NLCD include transportation, depending on the scale of your data, discontinuous roads and other stray pixels make for a noisy image. The Median filter (Filter/Noise/Median) in Photoshop permits the removal of unwanted pixels below a threshold of interest (Figure 19, upper right). Moving the radius setting to the right increases the amount of generalization. Be sure to apply the Median filter using nearest neighbor interpolation (Preferences/General/Image Interpolation) to prevent the urban colors from blurring.

Figure 19. Using the Median filter to generalize urban land cover data.

1. To start, open your land cover image in RGB or CMYK color mode and double check that Photoshop is set to use nearest neighbor interpolation (Preferences/General/Image Interpolation).
   
   
2. Select and delete all water pixels so they are now transparent (Figure 20, upper left).
   
   
3. Duplicate the land cover layer.
   
   
4. Select the Move tool in the Tool palette. Then on the keyboard press the up arrow cursor once. The image will move up one pixel.
   
   
5. Merge the copied layer with original below.
   
   
6. Duplicate the merged layer and repeat steps 4 and 5. But this time nudge the copied layer to the right.
   

Repeat this process two more times, nudging the copied layer down and then to the left respectively.

Figure 20. Using the Actions palette in Photoshop to spread shoreline pixels outward.


Each cycle of copying, nudging, and merging the image grows edge pixels outward by one pixel. Apply the steps repeatedly as needed until all misregistration gaps disappear. Alternatively, record your steps in the Actions palette and the save the results for one-click replays (Figure 20, bottom). We have built a Photoshop droplet (the new method for transfering actions to others) that automates this process. It is downloadable here for both Mac and PC.


Tip 5: Land cover removal

Just because a category for land cover exists doesn’t mean that you have to accept it. For example, the pixelized depiction of rivers and lakes is often too noisy and irregular for display on a map, requiring removal from the raster land cover data and showing it instead with vector lines in a drawing software application. Beyond issues of accuracy, considering that hundreds of thousands of pixels might be water on a land cover image, manually replacing them with the Clone Stamp tool is not a realistic option. The Dust & Scratches filter offers a quicker and more accurate solution. It reads the tonal contrast in an image and replaces pixels beyond a specified threshold with nearby unaffected pixels. In Figure 21, for example, the green forest color that dominates the image replaces the black lakes. Follow these steps to remove imbedded water from an image:

1. Select all water pixels and fill them with black.
   
   
2. Use the Dust & Scratches filter (Filter/Noise/Dust & Scratches) to infill the black-filled water bodies. (Be sure to use nearest neighbor interpolation.) Experiment with different radius and threshold settings until the black water bodies disappear. The settings will vary depending on the contrast range in your image.
   

Figure 21. Removing drainages from NLCD with the Dust & Scratches filter.