Linear symbols serve as the skeleton in maps and represent one of the primary carriers of map information, such as roads and rivers. They should be emphasized as key elements during map design. Given their narrow and elongated nature, linear symbols require enhanced color treatment to stand out. Therefore, highly saturated colors should be selected for line segments in linear symbol design. Different grades of linear symbols should be represented using colors with varying hues, brightness, and saturation levels. For instance, expressways, national highways, provincial roads, and county roads require distinct colors for differentiation. Special colors can be applied to certain lines, such as urban subway lines and contour lines. This section focuses on color design principles for common linear symbols in maps.
Roads
The road color schemes discussed here assume a gray-tinted basemap - a common basemap coloration. These principles may not apply to darker basemaps, requiring cartographers to adjust road colors according to specific basemap tones to achieve overall visual harmony.
Online maps like Map Hui, Baidu, Tianditu, and Tencent employ yellow-based color schemes for different road grades at 1:50,000 scale. These platforms generally use progressively lighter yellow tones corresponding to descending road grades. Notably, Tianditu uses purple for expressways while maintaining yellow for other road categories.
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| Figure: Color Settings for Different Road Grades in Web Maps |
At 1:2,000 scale, these online maps present more detailed road representations. Expressways, national highways, and provincial roads appear as double-line symbols while maintaining yellow-based color schemes. The border lines typically employ darker shades from the same color family to create subtle contrast with the central fill color.
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| Figure: Color Settings for Different Road Grades in Web Maps |
The prevalent use of yellow-based schemes for expressways, national highways, and lower-grade roads stems from yellow's psychological associations with brightness, optimism, and vitality. As the most prominent linear features on maps, roads benefit from these positive color connotations while enhancing aesthetic appeal.
However, yellow-based schemes may not be appropriate at all scales. When displaying dense urban street networks where roads aren't primary features, low-saturation colors like gray tones can reduce visual prominence.
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| Figure: Color Design for Urban Streets |
The above illustration demonstrates urban street color schemes at different scales. Single-line streets use gray (H=0, S=0, B=79), while double-line representations combine gray borders with white fills. These low-saturation schemes minimize visual clutter in complex urban road networks, improving map readability.
Rail
Digital maps typically represent railway lines with alternating gray-white patterns. The color scheme therefore involves two colors: gray and white. As shown below, the gray uses HSB values (H=0, S=0, B=79), where brightness (B value) can be adjusted to match overall map coloration.
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| Figure: Railway Lines |
Rivers
Water systems like rivers and lakes are universally associated with blue in cartographic representation, despite real-world variations in water color due to environmental factors. Digital maps therefore predominantly use blue-based schemes for water features. Different river grades can be distinguished through saturation and brightness variations, though most public digital maps use moderately saturated blue tones as shown below.
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| Figure: River Color Design |
Beyond roads, railways, and rivers, color design considerations extend to boundary lines (national borders, administrative divisions). National borders typically use gray tones, though distinctive colors may differentiate domestic and international boundaries. Administrative divisions (provincial, municipal, county) can be distinguished through variations in saturation/brightness within a color family or through different line patterns.
Related Topics:
Basic Characteristics of Color and Color Psychology
Color Design for Point Symbols
Color Design for Polygon Areas