Geospatial Data Types

The MARS runtime system is able to work with process geoinformation and geodata in multiple formats. Upon execution of a simulation, the data stored in such files are converted to graphs, consisting of nodes and edges.

GeoJSON

GeoJSON is a format for encoding a variety of geographic data structures. Typically, a set of data structures is held within a FeatureCollection made up of Features:

{ "type": "FeatureCollection",
  "features": [
    { "type": "Feature",
      "geometry": {"type": "Point", "coordinates": [102.0, 0.5]},
      "properties": {"prop0": "value0"}
    },
    { "type": "Feature",
      "geometry": {
        // insert geometry types here
      }
    },
    { "type": "Feature",
      "geometry": {
        // insert geometry types here
      }
    }
  ]
}

Below is a description of the geometry types supported in GeoJSON:

Point: a single point on a coordinate system.

Example:

{ "type": "Point",
    "coordinates": [30, 10]
}

LineString: a set of points connected by lines. 

{ "type": "LineString",
    "coordinates": [
        [30, 10], [10, 30], [40, 40]
    ]
}

The key coordinates contains a set of points, each of which connects to the one listed before it.

Polygon: a set of points connected by lines that form a closed shape.

{ "type": "Polygon",
    "coordinates": [
        [[35, 10], [45, 45], [15, 40], [10, 20], [35, 10]],
        [[20, 30], [35, 35], [30, 20], [20, 30]]
    ]
}

This is an example of a polygon within a polygon, creating a cut-out within the outer polygon. It is also possible to create a single filled-out polygon.

MultiPoint: a set of multiple unconnected points.

{ "type": "MultiPoint",
    "coordinates": [
        [10, 40], [40, 30], [20, 20], [30, 10]
    ]
}

MultiLineString: a set of multiple lines made up of multiple points.

{ "type": "MultiLineString",
    "coordinates": [
        [[10, 10], [20, 20], [10, 40]],
        [[40, 40], [30, 30], [40, 20], [30, 10]]
    ]
}

MultiPolygon: a set of polygons.

{ "type": "MultiPolygon",
    "coordinates": [
        [
            [[40, 40], [20, 45], [45, 30], [40, 40]]
        ],
        [
            [[20, 35], [10, 30], [10, 10], [30, 5], [45, 20], [20, 35]],
            [[30, 20], [20, 15], [20, 25], [30, 20]]
        ]
    ]
}

Here are examples of how these geometry types are represented visually:

Point LineString Polygon MultiPoint MultiLineString MultiPolygon
geojson_point geojson_linestring geojson_polygon2 geojson_multipoint geojson_multilinestring geojson_multipolygon


For more information on GeoJSON, please visit https://tools.ietf.org/html/rfc7946 or https://datatracker.ietf.org/wg/geojson/charter/.

GraphML

GraphML is an XML-based data format for representing graphs. For example, MARS can use geodata from a GraphML file to populate a VectorLayer or other layer type for agents to move on.

GraphML files that contain geodata can be generated using ODDI or osmnx. A useful tutorial on how to work with osmnx can be found here.

Note: GraphML cannot be visualized in QGIS.

Shapefile

Shapefile is a geospatial vector data format for GIS software that is also used within MARS runtime system models. They consist of multiple files, three of which are mandatory:

  1. .shp: shape format; the feature geometry itself
  2. .shx: shape index format; a positional index of the feature geometry to allow seeking forwards and backwards quickly
  3. .dbf: attribute format; columnar attributes for each shape, in dBase IV format

For more information on Shapefile specifications, please see the ESRI technical description.

Geopackage

GeoPackage is an open, standards-based, platform-independent, portable, compact format for transferring geospatial information. It contains data and geodata in a SQLite database file. For more information, please see the Geopackage homepage.