Some additions for data and tools

[jwoLondon]

Not sure if you prefer PRs or issues for suggested changes/additions, so am starting with an issue to log some proposed additions...

Under Data:

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OS OpenData

Ordnance Survey Open Data for Great Britain. Includes general topographic map data at a range of scales; useful thematic data such as greenspace, terrain, roads and rivers; postcode and place name georeferencing.

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Under Tools:

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Mapshaper

Useful for geospatial data processing in the browser such as file format conversion, map projection, feature simplification, filtering, clipping, merging etc. Can also be run locally from the command line.

Vega-Lite

Declarative visualization specification including cartographic output. Specifications can be written directly in JSON or via program language interfaces such as altair (Python) and elm-vegalite (Elm). See, for example, this tutorial on using OpenStreetMap with elm-vegalite

Vega

More flexible but lower-level declarative visualization specification including cartographic output. Specifications can be written directly in JSON or via program language interfaces such elm-vega.

Litvis

Literate Visualization notebook environment optimised for specifying visualizations and documenting the design process. While not specific to cartography, can be a useful environment for exploring cartographic design.

Observable

Reactive notebook environment for generation of visualization and cartographic output embedded in a textual narrative. Focus is on using d3 for specifying visual output.

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[tjukanovt]

Both are very welcome! Thank you!

[tjukanovt]

Added to main readme