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1.1.3. Minimum Dimensions

The symbolization of graphical objects for screen maps has to be adapted to the peculiarities of screens. Line widths, minimum sizes for point symbols and minimum distances between graphical elements have to be larger than on paper maps in order to be optically well discernible.

Line width

Line width (Brühlmeier 2000)

The picture on the left shows how lines with different line thicknesses are visualised on a screen. You might be surprised not to see the expected difference of the width of two lines. For example with the Adobe termSVG Viewers 3.0 and 6.0, line widths do not increase linearly, but grow irregularly. Lines between 0 and 0.3 pixels are always rendered with the same width and in gray colour. Between the pairs 0.3/0.4 pixel and 0.6/0.7 pixel differences of the apparent line width become recognizable. Other renderers may have completely different characteristics. (Räber et al. 2003)


You might ask yourself how it is possible to visualise a line that is smaller that one pixel which is the smallest element of a screen. If so, have a look at the popup window below.

Click here for more information

Minimum distances

Minimum distance between surfaces (Brühlmeier 2000) Minimum distance between lines of different widths (Brühlmeier 2000)

A series of test objects is used to identify the minimum distance between two surfaces. In order to unequivocally differentiate the two areas, they have to be separated by at least 1 pixel. A similar test can be done with lines to find the minimum distance for linear elements. As you can see in the right figure 1.5 pixel is that minimum distance. But for very thin lines the distance is 2 pixels, since they are rendered in grey. (Räber et al. 2003)
Recommended distances: between two surfaces: 1 Pixel; between two lines: 1.5 Pixel (for very thin lines: 2 pixels)

Dimension of point signatures

Minimum dimension of point signatures (Brühlmeier 2000)

Equally, the minimum areal dimensions of point signatures at which signatures can be identified unambiguously, can be examined. It is between 4 and 5 pixels. (Räber et al. 2003)
Recommended aerial dimension of point signatures: 4-5 Pixel


The distance the user keeps to the display device when studying a web map is approximately 80 cm, whereas a paper map is typically held at a distance of only 30 cm. In case of doubts, distances between map elements and minimum sizes of signatures should be chosen larger rather than smaller. (Räber et al. 2003)

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