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You can also see an overview of M4OPS on YouTube.

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Author Topic: GeoJSON - how we use it  (Read 1940 times)


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GeoJSON - how we use it
« on: 31 July 2016, 07:29:54 »
GeoJSON is a format based on JSON for encoding a variety of geographic data structures - Point, LineString, Polygon, MultiPoint, MultiLineString, and MultiPolygon. Geometric objects with additional properties are Feature objects. Sets of features are contained by FeatureCollection objects. See the spec .

This Wikipedia article describes GeoJSON, and this article is a very useful summary. A position is an array of coordinates in order: [longitude, latitude, elevation] (Note that many applications use the order latitude, longitude order - so beware!). GeoJSON can have four or more coordinates with undefined meaning, like time. Default projection is EPSG:4326. is an easy way of editing, viewing and updating GEOJSON files - a useful site. It uses mapbox markers (via token).

We use GeoJSON files to provide Feature Layers to M4OPS. These can come from many different places:
  • GIS systems like QGIS
  • public sources
  • saved by M4OPS itself (see the heading New Feature Layers)
  • hand-crafted in a text editor
We can also create GeoJSON files (just for points -  not lines or polygons) from CSV files (eg generated from our Access database for the HcN OPS). To do this:
  • the CSV file must be .csv, and have fields starting lon and lat
  • must use ; (semi-colon) for the separator (rather than comma) and must not use it in any text fields
  • can use empty fields but these are converted to “” (null becomes “null”, so do not use)
  • ? not use field names containing the letters "html"?
  • if generating from Access specify nothing round the text (not even ") and tick the option for field names in first row
  • drag and drop the CSV file onto and then save as GeoJSON
See also the list of GeoJSON utilities that will make your life easier.

VBA to JSON is possible ( but we have not used it.

For Edinburgh's Ainslie 1804, each Feature in a FeatureCollection has
  • "type": "Feature"
  • "properties":
    • "ID":
    • "PROPERTY":
  • "geometry":
    • "type": "MultiPolygon", "coordinates": etc
For HcN Pubs, we created the GeoJSON file by exporting a csv file of query MapFile01 and then dropping it onto
For HcN Census Entries we do similar.
« Last Edit: 31 July 2016, 07:57:07 by PeterC » is a Society for One-Place Studies project supported by Grassroots Giving from Skipton Building Society
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