Layers¶

Layers are the bedrock of GIFramework Maps. Without layers, your maps are basically useless.

Layers are pretty configurable, and have lots of various options, some of which are quite complex to set properly. For this reason, you should consider using the management interface if you can.

Relevant tables¶

Table Name	Description
Layer	Basic details about a published layer and how it can be used
LayerSource	Basic details about the source of a layer, including the type (TileWMS, XYZ etc.) and its attribution
LayerSourceOption	Contains the details about where a layer comes from and the options that will be applied to it
LayerSourceType	Lookup list describing the types of layers available. This should not be edited as it is tied directly to the application code
CategoryLayer	Mapping between layers and the categories they are added to

Adding a layer¶

Layers have two main parts to them, the Layer, and the Layer Source. When you add a layer, the first thing you do is define the Layer Source.

LayerSource¶

The LayerSource table contains very basic information about the layer.

Name - A friendly name for administrators.
Description - A basic description of the layer. This is shown to end users when the layer has no other description metadata available from source (see more about layer metadata below)
LayerSourceTypeId - The Id of the type of layer from the LayerSourceType table. This identifies the type of layer source this is. See LayerSourceType details below for more information.
AttributionId - The Id of the relevant Attribution that will be applied to this layer. Learn more about attributions in the attributions documentation

LayerSourceOption¶

The LayerSourceOption table contains the majority of the technical information required to show a layer. It is a one-to-many table, so one LayerSource can have many linked LayerSourceOptions, depending on the requirements of the layer. It is a simple key/value store with the following columns:

Name - This is the key, and should be set to one of the following understood values:
- url
- params
- cswendpoint
- projection
- tilegrid
Value - This is the value. See below for details on what this should contain
LayerSourceId - The Id of the relevant LayerSource that this option applies to

XYZ Layers¶

The only required option required for XYZ layers is url. This should be set to the URL endpoint for the service, with templates for the X, Y and Z portions. The provider normally provides this for you.

Example

https://api.os.uk/maps/raster/v1/zxy/layer/{z}/{x}/{y}.png

This assumes the layer is provided in the standard Spherical Mercator EPSG:3857 projection. If the service is providing tiles in a different projection, see the advanced configuration section below.

WMS layers¶

For WMS layers (TileWMS or ImageWMS), you need a minimum of url and params set.

url

This should be set to the 'base' url of the WMS service. This is normally provided to you by the service, and will look something like https://<service-url>/wms

params

This is a JSON object of additional parameters that are applied to the layer.

The params object should at a minimum contain the following

{
    "LAYERS": "LAYERNAME", 
    "FORMAT": "image/png", /*replace with required format*/
    "TILED":"true"
}

These parameters will be used by OpenLayers to make appropriate requests to the service. Additional parameters as required by the service can be added be appending them onto the JSON object.

Common additional parameters you may want to use include:

CQL_FILTER - Will apply a CQL filter to the layer
STYLES - Will set the style of the layer to a specific style available to the server
AUTHKEY - If the service uses AUTHKEY authentication (or any other type of key based authentication)

Warning

Incorrectly formatting this JSON object can result in the layer or the entire map failing to load correctly. Edit with caution.

Vector layers¶

For vector layers, you will need a minimum of the url option. Additionally, unless you want the default OpenLayers styles, you will need a style option as well. See Styling vector layers for more information.

Additional options include: - typename - When using a WFS service, you should set the url to the base server URL, and the typename as the layer name you are requesting - format - The format the data is in. Defaults to 'application/json' unless specified. - loadingstrategy - Can be bbox or all. This defines how the vector layer is loaded, either with a bbox strategy (loading just a bounding box worth of data at a time) or loading everything at once. In reality, WFS based layers will default to bbox unless specifically set to all, and non-WFS layers will default to all

Supported vector formats

JSON (application/json, text/json, geojson or json)
GML3 (text/xml; subtype=gml/3.1.1, gml3)
GML2 (text/xml; subtype=gml/2.1.2, gml2)
KML (application/vnd.google-earth.kml xml, application/vnd.google-earth.kml+xml, kml)

Limitation

Vectors cannot have a filter pre-applied to them.

Other options¶

projection - If the layer is only available in a projection that is not the same as the map you are putting it in to, set the projection here, otherwise you can not include it, and the layer will be requested in the projection of the map. For XYZ layers, see the section on XYZ reprojection

Layer¶

A layer first requires a layer source to be created that defines where the layer comes from.

Once this has been created, the layer table has the following fields to fill in:

Name - The friendly name that will appear in the layer control
LayerSourceId - The Id from the LayerSource table
BoundId - An optional Id from the Bound table that defines what the max extent of this layer is. Setting this prevents GIFramework Maps from requesting tiles or doing feature requests outside of the set bounds. This improves performance and efficiency, but is not required. Leave blank for no restriction
MaxZoom - The maximum zoom this layer will be turned on for, for example if set to 15, the layer will turn off once you zoom in past level 15. Set to blank for no restriction
MinZoom - As above, but the other way round, for example if set to 12, the layer will turn off once you zoom out past level 12
ZIndex - This is the 'layer order' on the map. Higher numbers will, by default, appear above lower numbers when both layers are turned on. For things like Aerial Photography, this should generally be set very low (such as -500). Leave blank for default of 0
DefaultOpacity - The default opacity (or transparency) of the layer between 0 (invisible) and 100 (opaque). Leave blank for default of 100
DefaultSaturation - The default saturation of the layer between 0 (greyscale) and 100 (full colour). Leave blank for default of 100
InfoTemplate - The template for what appears when you select a single map feature.. See Info Templates below for more information
InfoListTitleTemplate - The template for what appears when you click multiple items and are presented with a list of features. See Info Templates below for more information
Queryable - A Boolean indicating whether the user is allowed to query (info click) this layer
DefaultFilterEditable - A Boolean indicating if the user is allowed to edit any filters already applied to the layer in the layer source
Filterable - A Boolean indicating if the user is allowed to apply filters to this layer
ProxyMapRequests - A Boolean indicating if all GetMap requests should be proxied via the application proxy. Only use this if a remote layer can't handle CORS requests (errors will appear in the console and layer control when using this layer if this is the case). See Proxying for more details
ProxyMetaRequests - As above, but related to all metadata and query requests, such as GetCapabilities and GetFeatureInfo. See Proxying for more details

Info Templates¶

See 'Creating info templates'

CategoryLayer¶

The CategoryLayer table defines which layers are available in which categories.

LayerId - The Id from the Layer table
CategoryId - The Id from the Category table
SortOrder - The position this layer should appear within this category

LayerSourceType¶

There are currently 7 supported layer types in GIFramework Maps. More may be added in the future.

XYZ¶

The XYZ source is used for tile data that is accessed through URLs that include a zoom level and tile grid x/y coordinates. Examples include OpenStreetMap and OpenCycleMap.

TileWMS¶

The TileWMS source is used for WMS layers that are provided 'tiled', normally in 256px squares.

This is normally the best option, as it is more efficient and quicker, and can be cached by the users browser, but it can sometimes have issues with labels, or some services might not provide it. In these cases, use ImageWMS.

ImageWMS¶

The ImageWMS source is used for WMS layers that are provided 'untiled', so a single image is returned for the entire map screen. Normally you would choose TileWMS when available, but ImageWMS is particularly good if you have labels, or, if the layer is very complex, a single tile can load quicker than many smaller tiles.

Vector¶

The Vector source is used for WFS layers or file based layers (such as a KML or GeoJSON file at a specific URL). Currently, GIFramework Maps can handle GML2, GML3, GeoJSON, JSON and KML formats as a vector source. This source type uses standard vector rendering, so is very precise and can handle things like rotating labels, but because of this it is not suitable for large datasets or those with complex geometries.

VectorImage¶

The VectorImage source is fundamentally the same as the Vector source, but can handle larger datasets and geometries slightly better, by rendering the vector as an image on the client. This does mean some sharpness is occasionally lost, and things like labels don't rotate, but its much less 'laggy' when moving the map around with large or complex datasets.

VectorTile¶

The VectorTile source is used to render VectorTiles, a common format for things like basemaps which splits vectors up into tiles and delivers them efficiently to the browser (learn more). MVT (Mapbox Vector Tiles) is the most common standard for this.

OGC VectorTile¶

The OGC VectorTile format is the new OGC standard for VectorTiles. It works in a similar way to VectorTiles, but is the standard promoted by the Open Geospatial Consortium.

Advanced configuration¶

XYZ reprojection¶

XYZ layers can be provided in different projections. To make use of on the fly reprojection, you need to provide an appropriate tilegrid option, describing the resolutions and origins of the XYZ layer. The service provider should be able to provide this.

Example

The `tilegrid' for British National Grid EPSG:27700 is

{
    "resolutions": [896.0, 448.0, 224.0, 112.0, 56.0, 28.0, 14.0, 7.0, 3.5, 1.75],
    "origin": [-238375.0, 1376256.0]
}