Read and write spatial data

The table below lists the spatial file formats that are supported for reading and writing operations with the Spatial IO module.

Data Format Read Write
GeoJSON
GeoRSS
GML
GPX
KML
KMZ
Spatial CSV
Well-Known Text

These next sections outline all the different tools for reading and writing spatial data using the Spatial IO module.

Read spatial data

The atlas.io.read function is the main function used to read common spatial data formats such as KML, GPX, GeoRSS, GeoJSON, and CSV files with spatial data. This function can also read compressed versions of these formats, as a zip file or a KMZ file. The KMZ file format is a compressed version of KML that can also include assets such as images. Alternatively, the read function can take in a URL that points to a file in any of these formats. URLs should be hosted on a CORS enabled endpoint, or a proxy service should be provided in the read options. The proxy service is used to load resources on domains that aren't CORS enabled. The read function returns a promise to add the image icons to the map, and processes data asynchronously to minimize impact to the UI thread.

When reading a compressed file, either as a zip or a KMZ, it will be unzipped and scanned for the first valid file. For example, doc.kml, or a file with other valid extension, such as: .kml, .xml, geojson, .json, .csv, .tsv, or .txt. Then, images referenced in KML and GeoRSS files are preloaded to ensure they're accessible. Inaccessible image data may load an alternative fallback image or will be removed from the styles. Images extracted from KMZ files will be converted to data URIs.

The result from the read function is a SpatialDataSet object. This object extends the GeoJSON FeatureCollection class. It can easily be passed into a DataSource as-is to render its features on a map. The SpatialDataSet not only contains feature information, but it may also include KML ground overlays, processing metrics, and other details as outlined in the following table.

Property name Type Description
bbox BoundingBox Bounding box of all the data in the data set.
features Feature[] GeoJSON features within the data set.
groundOverlays (atlas.layer.ImageLayer | atlas.layers.OgcMapLayer)[] An array of KML GroundOverlays.
icons Record<string, string> A set of icon URLs. Key = icon name, Value = URL.
properties any Property information provided at the document level of a spatial data set.
stats SpatialDataSetStats Statistics about the content and processing time of a spatial data set.
type 'FeatureCollection' Read-only GeoJSON type value.

Examples of reading spatial data

The following code shows how to read a spatial data set, and render it on the map using the SimpleDataLayer class. The code uses a GPX file pointed to by a URL.


The next code demo shows how to read and load KML, or KMZ, to the map. KML can contain ground overlays, which will be in the form of an ImageLyaer or OgcMapLayer. These overlays must be added on the map separately from the features. Additionally, if the data set has custom icons, those icons need to be loaded to the maps resources before the features are loaded.


You may optionally provide a proxy service for accessing cross domain assets that may not have CORS enabled. The read function will try to access files on another domain using CORS first. After the first time it fails to access any resource on another domain using CORS it will only request additional files if a proxy service has been provided. The read function appends the file URL to the end of the proxy URL provided. This snippet of code shows how to pass a proxy service into the read function:

//Read a file from a URL or pass in a raw data as a string.
atlas.io.read('https://nonCorsDomain.example.com/mySuperCoolData.xml', {
    //Provide a proxy service
    proxyService: window.location.origin + '/YourCorsEnabledProxyService.ashx?url='
}).then(async r => {
    if (r) {
        // Some code goes here . . .
    }
});

The demo below shows how to read a delimited file and render it on the map. In this case, the code uses a CSV file that has spatial data columns.


Write spatial data

There are two main write functions in the spatial IO module. The atlas.io.write function generates a string, while the atlas.io.writeCompressed function generates a compressed zip file. The compressed zip file would contain a text-based file with the spatial data in it. Both of these functions return a promise to add the data to the file. And, they both can write any of the following data: SpatialDataSet, DataSource, ImageLayer, OgcMapLayer, feature collection, feature, geometry, or an array of any combination of these data types. When writing using either functions, you can specify the wanted file format. If the file format isn't specified, then the data will be written as KML.

The tool below demonstrates the majority of the write options that can be used with the atlas.io.write function.


Example of writing spatial data

The following sample allows you to drag and drop and then load spatial files on the map. You can export GeoJSON data from the map and write it in one of the supported spatial data formats as a string or as a compressed file.


You may optionally provide a proxy service for accessing cross domain assets that may not have CORS enabled. This snippet of code shows you could incorporate a proxy service:

atlas.io.read(data, {
    //Provide a proxy service
    proxyService: window.location.origin + '/YourCorsEnabledProxyService.ashx?url='
}).then(
    //Success
    function(r) {
        //some code goes here ...
    }
);

Read and write Well-Known Text (WKT)

Well-Known Text (WKT) is an Open Geospatial Consortium (OGC) standard for representing spatial geometries as text. Many geospatial systems support WKT, such as Azure SQL and Azure PostgreSQL using the PostGIS plugin. Like most OGC standards, coordinates are formatted as "longitude latitude" to align with the "x y" convention. As an example, a point at longitude -110 and latitude 45 can be written as POINT(-110 45) using the WKT format.

Well-known text can be read using the atlas.io.ogc.WKT.read function, and written using the atlas.io.ogc.WKT.write function.

Examples of reading and writing Well-Known Text (WKT)

The following code shows how to read the well-known text string POINT(-122.34009 47.60995) and render it on the map using a bubble layer.


The following code demonstrates reading and writing well-known text back and forth.


Read and write GML

GML is a spatial XML file specification that's often used as an extension to other XML specifications. GeoJSON data can be written as XML with GML tags using the atlas.io.core.GmlWriter.write function. The XML that contains GML can be read using the atlas.io.core.GmlReader.read function. The read function has two options:

  • The isAxisOrderLonLat option - The axis order of coordinates "latitude, longitude" or "longitude, latitude" can vary between data sets, and it isn't always well defined. By default the GML reader reads the coordinate data as "latitude, longitude", but setting this option to true will read it as "longitude, latitude".
  • The propertyTypes option - This option is a key value lookup table where the key is the name of a property in the data set. The value is the object type to cast the value to when parsing. The supported type values are: string, number, boolean, and date. If a property isn't in the lookup table or the type isn't defined, the property will be parsed as a string.

The atlas.io.read function will default to the atlas.io.core.GmlReader.read function when it detects that the input data is XML, but the data isn't one of the other support spatial XML formats.

The GmlReader will parse coordinates that has one of the following SRIDs:

  • EPSG:4326 (Preferred)
  • EPSG:4269, EPSG:4283, EPSG:4258, EPSG:4308, EPSG:4230, EPSG:4272, EPSG:4271, EPSG:4267, EPSG:4608, EPSG:4674 possibly with a small margin of error.
  • EPSG:3857, EPSG:102100, EPSG:3785, EPSG:900913, EPSG:102113, EPSG:41001, EPSG:54004

More resources

Learn more about the classes and methods used in this article:

atlas.io static functions

SpatialDataSet

SpatialDataSetStats

GmlReader

GmlWriter

atlas.io.ogc.WKT functions

Connect to a WFS service

Leverage core operations

Supported data format details

Next steps

See the following articles for more code samples to add to your maps:

Add an OGC map layer