User:Hesperian/Notes/Cartographic design

These are guidelines for cartographic design that I gleaned from Robinson, A. et al. (1995) Elements of Cartography, Sixth Edition, as applicable to Wikipedia.

Symbol size

Point symbols are generally harder to see than line symbols and area symbols.

For point symbols, people can generally read symbols that subtend at least one minute of arc of their view. Any smaller, and they can't pick it up. It is best to make symbols a good deal bigger than that, say 2 minutes of arc.

The minimum specifiable default thumb size for Wikipedia is 120px, which typically would be about 3 1/2 centimetres wide on the screen. It is not unreasonable to expect these people with extremely small default thumb sizes to lean forward to within about 20 centimetres of their screen, and even then they should expect symbols to be at the limit of recognition. i.e. 1 minute of arc. This equates to about 0.05 millimetres, or 1/600 of the image width. But of course any smaller than 1/120 of the image width equates to a single pixel, so there's no point going any smaller than that.

A more typical default thumb size, indeed the default default, is 180px, which typically would be about 5 centimetres wide on screen. Ideally these people should be able to interpret a symbol comfortably, i.e. in 2 minutes of arc, from a comfortable distance, say 60 centimetres. In this case, symbols would have to be about 0.35 of a millimetre, or 1/140th of the image width.

So the ballpark figure is that symbols should be no smaller than about 1/120th of the width of an image.

Colours

Blue is always for water. Green is generally for vegetation. Brown is generally for land surface features. Yellow or tan is for dry, sparsely vegetated areas. Deviation from these conventions usually causes confusion.

When progressions of colour are used to indicate magnitude, darker generally means more.

Textures

When textures are used to indicate magnitude, denser generally means more.

Less than 16 lines per centimetre is generally considered too sparse to carry a magnitude value. More than 30 lines per centimetre is generally considered too dense to carry a magnitude value. Magnitudes should therefore be expressed by textures that run between these two values. In Wikipedia terms, this is not very helpful, as it suggests that textures should range from a line every 2 pixels to a line every 1 pixel. The inevitable conclusion is that the use of textures to indicate magnitude simply doesn't work in small images like the ones we typically use.

Parallel line patterns are annoying. Especially vertical ones.

Typography

Type

The use of different fonts and forms to indicate feature classes is generally a waste of effort. Stick with a few forms of a single font.

Generally, hydrographic, landform and other natural features are labelled in italics, whereas features created by humans are labelled in Roman. This is a strong convention for water features, not so strong for others.

Text placement

Text should be entirely on land or entirely on water.

If the names and the data clash, then the data should be interrupted, not the name.

Wherever possible, point text should match the orientation of the map, which usually means it should be horizontal, or in line with parallels.

If it is necessary to use disoriented lettering, it should be set in a slight curve.

Text labels for points should be placed in the first available of the following positions:

1. on the right, raised;
2. on the left, raised;
3. on the right, lowered;
4. on the left, lowered;
5. centred on top;
6. centred beneath;
7. on top, shifted right;
8. beneath, shifted right;
9. on top, shifted left;
10. beneath, shifted left.

Names should be letter-spaced as little as possible for point labels.

The names of a linear feature should run alongside that feature. They are lightly better above than below.

If a linear feature is vertical, it is easier to read text that reads upwards on the left, than downwards on the right.

Names of areal features should appear within the boundary of the feature. The should be letterspaced to extend across the area if possible.

Other

The visual centre of a map is about 5% higher than the physical centre. The features of the map should be balanced about this centre.

If a map has a conventional north-up orientation, than a direction indicator is unnecessary.