Tuesday, 21 April 2020

OS Open Map Local Styling

This second Find data blogpost is to explain how Ordnance Survey created a stylesheet to make the Open Map Local backdrop style map not only visually pleasing, but easy to understand as well

Stylesheet is code that, when applied to geographic data, determines the visual appearance of the content. Once added in Geoserver and connected to the relevant layers, a proper map can be displayed through a WMS feed.

To style OS Open Map Local in the ‘backdrop’ theme, different stylesheets are requested for each layer depending of geometry and classification - building, river, road, etc. In this blogpost, polygon with building, line with road and points with London Underground logo will be presented and explained.

For building, the stylesheet is simple with just minimum and maximum scale limit and color defined by HEX code color.


To style line data as roads, minimum and maximum scale rules are used. The rule for A Road is defined with the LineSymbolizer. Color is specified via HEX code color, width of line in pixel (12 pixels), stroke-linecap parameter renders the ends of line as rounded instead of flat and the stroke-linejoin parameter renders the junction with other line as rounded.
Label is set with TextSymbolizer with different parameters: Font, LabelPlacement, Halo, Fill, VendorOption.

Font set identifies font family, font size and font weight.
LabelPlacement set defines label position in regard to the line in pixels. In the case of A Roads PerpendicularOffset is set to the default, which is 0. A positive value displaces upwards, a negative value downwards.
Halo set characterizes a halo around the font with radius in pixels and fill with HEX code color.
Fill set identifies label color with HEX code color.
Vendor option sets is a Geoserver specific option composed of multiple parameters.
  • spaceAround allow labels to overlap (negative value) or add extra space around labels (positive value)
  • followLine forces the labels to follow the curve of the line
  • Group allows display of a single label for multiple features in a logical group
  • maxAngleDelta sets the maximum angle, in degrees, between two characters. Used in conjunction with followLine.
  • maxDisplacement controls the displacement of the label along the line. This option avoids conflict by using alternate location with pixels along the line.
  • Repeat defines how often a label is displayed along a line.

London Underground Station:

To style a point with the London underground logo, the stylesheet uses a link to an external SVG file which contains the London underground logo. In this case only minimum and maximum scale are determined and SVG size. This method can be used for any complex object that cannot be created using standard stylesheets.

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