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GPS Mapping Software - Exporting map data to a GeoJSON file - Tutorial

Introduction

GeoJSON is a format for encoding a variety of geographic data structures. A GeoJSON object may represent a geometry, a feature, or a collection of features. GeoJSON supports the following geometry types: Point, LineString, Polygon, MultiPoint, MultiLineString, MultiPolygon, and GeometryCollection. Features in GeoJSON contain a geometry object and additional properties, and a feature collection represents a list of features.

GeoJSON is based on JSON, which stands for JavaScript Object Notation. The Eye4Software GPS Mapping Studio is able to both import and export GeoJSON files. This document describes how to export GeoJSON data.

{ "type": "FeatureCollection",
  "features": [
      { "type": "Feature",
        "geometry": {"type": "Point", "coordinates": [-112.13367, 36.04988]},
        "properties": {"name": "Grand Canyon"}
      }
   ]
}

Example of a GeoJSON file containing a sinle point and attribute

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Loading the source data

Only vector maps can be converted to a GeoJSON file. It is not possible to convert raster data to a GeoJSON file, because they do contain pixel data instead of features. You can create a vector map by importing one of the supported vector formats, like ESRI shape file, AutoCad DXF, USGS DLG files, Arc/Info export data, OpenStreetMap file or any other supported vector format. You can import the source vector map by selecting "Import" => "Import Map..." from the "File" menu. If the vector map has been loaded successfully, the map will be displayed on the screen, and the map name will appear in the "Project Explorer".

click on the image to enlarge

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Exporting the map

In order to export a vector map, just right-click the map name in the "Project Explorer", and select the "Export Map..." option from the popup menu, as showed in the image below. If the "Project Explorer" isn't visible, you can show it by selecting "Project Explorer" from the "View" menu.

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Export Vector Data Dialog

After selecting the "Export Map..." option, the following dialog will appear:

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Selecting source data

Use the first drop down box to select the source data to be exported. By default, the selected map is displayed, but you will also be able to select other vector maps. Please note that raster maps are not displayed, because they cannot be exported as a vector format. When the "Export Vector Data" dialog is selected by right clicking on the desired vector map, you do not have to change this value.

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Set destination options

The second part of the dialog can be used to specify the output settings, like format, filename and other options. To export the map data as GeoJSON file, select the "GeoJSON Map File (*.geojson)" option from the "Format" drop down box.

Now we have to select an output file. You can use the "Browse..." button to select a location to store the file, or you can just enter it by hand. With GeoJSON, all information is stored in a single (json or geojson) file. Before creating the file, the software will check whether the file location is accesible/writable.

Depending on the choosen export format, selectable options will appear. When GeoJSON is selected, the "Export Attributes" option is checked and you are not able to uncheck it. This is because attribute fields are required, otherwise some software will not be able to read the file.

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Set Projection

The third section of the dialog allows you to set the projection used in the file. When you are writing a format that does not support other projections, this section will be disabled. For GeoJSON files however, it is possible to select a projection used to write the features. Using this feature, the GPS Mapping Studio can be used to convert vector maps from one map projection to another. By default the current map projection is selected. Please note that when selecting a map projection not suitable for the loaded map, distortion will occur.

click on the image to enlarge

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Exporting the map

Just click "OK" to start the export. For small files, this takes only a couple of seconds, for big files it can take a couple of minutes. You can watch the progress in the statusbar at the bottom of the screen.

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