WMSLayer

A flattened collection of all WMSSublayers based on the sublayers property.

Blend modes are used to blend layers together to create an interesting effect in a layer, or even to produce what seems like a new layer. Unlike the method of using transparency which can result in a washed-out top layer, blend modes can create a variety of very vibrant and intriguing results by blending a layer with the layer(s) below it.

When blending layers, a top layer is a layer that has a blend mode applied. All layers underneath the top layer are background layers. The default blending mode is normal where the top layer is simply displayed over the background layer. While this default behavior is perfectly acceptable, the use of blend modes on layers open up a world of endless possibilities to generate creative maps.

The layers in a GroupLayer are blended together in isolation from the rest of the map.

In the following screenshots, the vintage shaded relief layer is displayed over a firefly world imagery layer. The color blend mode is applied to the vintage shaded relief and the result looks like a new layer.

The following factors will affect the blend result:

• Order of all layers
• Layer opacity
• Opacity of features in layers
• Visibility of layers
• By default, the very bottom layer in a map is drawn on a transparent background. You can change the MapView's background color.

Blend mode	Description
normal	The top layer is displayed over the background layer. The data of the top layer block the data of background layer where they overlap.
average	Takes the mathematical average of top and background layers. Result of average blend mode is often similar to the effect of setting the layer's opacity to 50%.

Lighten blend modes:

The following blend modes create lighter results than all layers. In lighten blend modes, pure black colors in the top layer become transparent allowing the background layer to show through. White in the top layer will stay unchanged. Any color that is lighter than pure black is going to lighten colors in the top layer to varying degrees all way to pure white.

Lighten blend modes can be useful when lightening dark colors of the top layer or removing black colors from the result. The plus, lighten and screen modes can be used to brighten layers that have faded or dark colors on a dark background.

Blend mode	Description
lighten	Compares top and background layers and retains the lighter color. Colors in the top layer become transparent if they are darker than the overlapping colors in the background layer allowing the background layer to show through completely. Can be thought of as the opposite of darken blend mode.
lighter	Colors in top and background layers are multiplied by their alphas (layer opacity and layer's data opacity. Then the resulting colors are added together. All overlapping midrange colors are lightened in the top layer. The opacity of layer and layer's data will affect the blend result.
plus	Colors in top and background layers are added together. All overlapping midrange colors are lightened in the top layer. This mode is also known as add or linear-dodge.
screen	Multiplies inverted colors in top and background layers then inverts the colors again. The resulting colors will be lighter than the original color with less contrast. Screen can produce many different levels of brightening depending on the luminosity values of the top layer. Can be thought of as the opposite of the multiply mode.
color-dodge	Divides colors in background layer by the inverted top layer. This lightens the background layer depending on the value of the top layer. The brighter the top layer, the more its color affects the background layer. Decreases the contrast between top and background layers resulting in saturated mid-tones and blown highlights.

Darken blend modes:

The following blend modes create darker results than all layers. In darken blend modes, pure white in the top layer will become transparent allowing the background layer to show through. Black in the top layer will stay unchanged. Any color that is darker than pure white is going to darken a top layer to varying degrees all the way to pure black.

The multiply blend mode is often used to highlight shadows, show contrast, or accentuate an aspect of a map. For example, you can use multiply blend mode on a topographic map displayed over hillshade when you want to have your elevation show through the topographic layer. See the intro to layer blending sample.

The multiply and darken modes can be used to have dark labels of the basemap to show through top layers. See the darken blending sample.

The color-burn mode works well with colorful top and background layers since it increases saturation in mid-tones. It increases the contrast by tinting pixels in overlapping areas in top and bottom layers more towards the top layer color. Use this blend mode, when you want an effect with more contrast than multiply or darken.

The following screenshots show how the multiply blend mode used for creating a physical map of the world that shows both boundaries and elevation.

Blend mode	Description
darken	Emphasizes the darkest parts of overlapping layers. Colors in the top layer become transparent if they are lighter than the overlapping colors in the background layer, allowing the background layer to show through completely.
multiply	Emphasizes the darkest parts of overlapping layers by multiplying colors of the top layer and the background layer. Midrange colors from top and background layers are mixed together more evenly.
color-burn	Intensifies the dark areas in all layers. It increases the contrast between top and background layers, by tinting colors in overlapping area towards the top color. To do this it inverts colors of the background layer, divides the result by colors of the top layer, then inverts the results.

Contrast blend modes:

The following blend modes create contrast by both lightening the lighter areas and darkening the darker areas in the top layer by using lightening or darkening blend modes to create the blend. The contrast blend modes will lighten the colors lighter than 50% gray ([128,128,128]), and darken the colors darker than 50% gray. 50% gray will be transparent in the top layer. Each mode can create a variety of results depending on the colors of top and background layers being blended together. The overlay blend mode makes its calculations based on the brightness of the colors in the background layer while all of the other contrast blend modes make their calculations based on the brightness of the top layer. Some of these modes are designed to simulate the effect of shining a light through the top layer, effectively projecting upon the layers beneath it.

Contrast blend modes can be used to increase the contrast and saturation to have more vibrant colors and give a punch to your layers. For example, you can duplicate a layer and set overlay blend mode on the top layer to increase the contrast and tones of your layer. You can also add a polygon layer with a white fill symbol over a dark imagery layer and apply soft-light blend mode to increase the brightness in the imagery layer.

The following screenshots show an effect of the overlay blend mode on a GraphicsLayer. The left image shows when the buffer graphics layer has the normal blend mode. As you can see, the gray color for the buffer polygon is blocking the intersecting census tracts. The right image shows when the overlay blend mode is applied to the buffer graphics layer. The overlay blend mode darkens or lightens the gray buffer polygon depending on the colors of the background layer while the census tracts layer is shining through. See this in action.

Normal blend mode	Overlay blend mode

Blend mode	Description
overlay	Uses a combination of multiply and screen modes to darken and lighten colors in the top layer with the background layer always shining through. The result is darker color values in the background layer intensify the top layer, while lighter colors in the background layer wash out overlapping areas in the top layer.
soft-light	Applies a half strength screen mode to lighter areas and half strength multiply mode to darken areas of the top layer. You can think of the soft-light as a softer version of the overlay mode.
hard-light	Multiplies or screens the colors, depending on colors of the top layer. The effect is similar to shining a harsh spotlight on the top layer.
vivid-light	Uses a combination of color-burn or color-dodge by increasing or decreasing the contrast, depending on colors in the top layer.

Component blend modes:

The following blend modes use primary color components, which are hue, saturation and luminosity to blend top and background layers. You can add a feature layer with a simple renderer over any layer and set hue, saturation, color or luminosity blend mode on this layer. With this technique, you create a brand new looking map.

The following screenshots show where the topo layer is blended with world hillshade layer with luminosity blend mode. The result is a drastically different looking map which preserves the brightness of the topo layer while adapting the hue and saturation of the hillshade layer.

Blend mode	Description
hue	Creates an effect with the hue of the top layer and the luminosity and saturation of the background layer.
saturation	Creates an effect with the saturation of the top layer and the hue and luminosity of the background layer. 50% gray with no saturation in the background layer will not produce any change.
luminosity	Creates effect with the luminosity of the top layer and the hue and saturation of the background layer. Can be thought of as the opposite of color blend mode.
color	Creates an effect with the hue and saturation of the top layer and the luminosity of the background layer. Can be thought of as the opposite of luminosity blend mode.

Composite blend modes:

The following blend modes can be used to mask the contents of top, background or both layers.

• Destination modes are used to mask the data of the top layer with the data of the background layer.
• Source modes are used to mask the data of the background layer with the data of the top layer.

The destination-in blend mode can be used to show areas of focus such as earthquakes, animal migration, or point-source pollution by revealing the underlying map, providing a bird’s eye view of the phenomenon. Check out multiple blending and groupLayer blending samples to see composite blend modes in action.

The following screenshots show feature and imagery layers on the left side on their own in the order they are drawn in the view. The imagery layer that contains land cover classification rasters. The feature layer contains 2007 county crops data. The right image shows the result of layer blending where destination-in blendMode is set on the imagery layer. As you can see, the effect is very different from the original layers. The blended result shows areas of cultivated crops only (where both imagery and feature layers overlap).

Blend mode	Description
destination-over	Destination/background layer covers the top layer. The top layer is drawn underneath the destination layer. You'll see the top layer peek through wherever the background layer is transparent or has no data.
destination-atop	Destination/background layer is drawn only where it overlaps the top layer. The top layer is drawn underneath the background layer. You'll see the top layer peek through wherever the background layer is transparent or has no data.
destination-in	Destination/background layer is drawn only where it overlaps with the top layer. Everything else is made transparent.
destination-out	Destination/background layer is drawn where it doesn't overlap the top layer. Everything else is made transparent.
source-atop	Source/top layer is drawn only where it overlaps the background layer. You will see the background layer peek through where the source layer is transparent or has no data.
source-in	Source/top layer is drawn only where it overlaps with the background layer. Everything else is made transparent.
source-out	Source/top layer is drawn where it doesn't overlap the background layer. Everything else is made transparent.
xor	Top and background layers are made transparent where they overlap. Both layers are drawn normal everywhere else.

Invert blend modes:

The following blend modes either invert or cancel out colors depending on colors of the background layer. These blend modes look for variations between top and background layers. For example, you can use difference or exclusion blend modes on two imagery layers of forest covers to visualize how forest covers changed from one year to another.

The invert blend mode can be used to turn any light basemap into a dark basemap to accommodate those who work in low-light conditions. The following screenshots show how setting the invert blend mode set on a feature layer with a simple renderer turns the world terrain basemap into a dark themed basemap in no time.

Blend mode	Description
difference	Subtracts the darker of the overlapping colors from the lighter color. When two pixels with the same value are subtracted, the result is black. Blending with black produces no change. Blending with white inverts the colors. This blending mode is useful for aligning layers with similar content.
exclusion	Similar to the difference blend mode, except that the resulting image is lighter overall. Overlapping areas with lighter color values are lightened, while darker overlapping color values become transparent.
minus	Subtracts colors of the top layer from colors of the background layer making the blend result darker. In the case of negative values, black is displayed.
invert	Inverts the background colors wherever the top and background layers overlap. The invert blend mode inverts the layer similar to a photographic negative.
reflect	This blend mode creates effects as if you added shiny objects or areas of light in the layer. Black pixels in the background layer are ignored as if they were transparent.

Copyright information for the WMS service. This defaults to the value of the AccessConstraints property from the GetCapabilities request.

Use this to append different custom parameters to the WMS map requests. The custom layer parameters are applied to GetMap and GetFeatureInfo.

Use this to append custom parameters to all WMS requests. The custom parameters are applied to GetCapabilities, GetMap and GetFeatureInfo. For example, if an access key is required, the key can be configured as a custom parameter. The layer's refresh() method needs to be called if the customParameters are updated at runtime.

Description for the WMS layer. This defaults to the value of the Abstract property from the WMS GetCapabilities request.

An array of time, elevation and other dimensions for the root layer. Information from a TimeDimension can be used to update View.timeExtent, WMSLayer.timeExtent, or to configure a TimeSlider widget.

A WMSLayer or WMSSublayer can only have one time dimension. The following example shows how to find the time dimension (if any) for the base layer.

const layer = new WMSLayer({
  url: "https://public-wms.met.no/verportal/verportal.map?request=GetCapabilities&service=WMS&version=1.3.0"
});
await layer.load();
const timeDimension = layer.dimensions.find((dimension) => dimension.name === "time");

Data can exist at specific times or time ranges. We can access this information from the extent property of the TimeDimension as either an array of discrete dates or TimeDimensionIntervals. For example, continuing from the previous example, a TimeSlider is configured using the extent from a TimeDimension.

const dates = timeDimension.extent; // This time dimension is expressed as an array of dates.
const start = dates[0]; // Get the first and earliest date
const end = dates[dates.length -1]; // Get last date
const timeSlider = new TimeSlider({
  container: "timeSliderDiv",
  view: view,
  mode: "instant",
  timeVisible: true,
  loop: true,
  fullTimeExtent: { // The TimeSlider UI will span all dates
    start,
    end
  },
  stops: {
    dates // The TimeSlider thumb will snap exactly to each valid date
  }
})

Effect provides various filter functions that can be performed on the layer to achieve different visual effects similar to how image filters work. This powerful capability allows you to apply css filter-like functions to layers to create custom visual effects to enhance the cartographic quality of your maps. This is done by applying the desired effect to the layer's effect property as a string or an array of objects to set scale dependent effects.

The MIME type that will be requested by popups.

The only valid values are "text/html" and "text/plain" or whichever is support by the service with "text/html" being preferred. For a list of all supported MIME types please refer to featureInfoFormats.

This property lists all available MIME-types that can be used with the WMS service's GetFeatureInfo request. The GetFeatureInfo request is indirectly used by popups.

To take advantage of unsupported MIME-types, such as application/json, please refer to fetchFeatureInfoFunction.

The URL for the WMS GetFeatureInfo call.

Function to override the default popup behavior of WMSLayer.

By default, popups will make a GetFeatureInfo request specifying the featureInfoFormat mime-type. The featureInfoFormat property only supports text/plain or text/html.

Use fetchFeatureInfoFunction to take advantage of other mime-types supported by the service such as JSON or GeoJSON. See featureInfoFormats) for a list of supported mime-types.

All bounding boxes defined for the layer.

The map image format (MIME type) to request. Defaults to image/png if the WMS service supports it. If not, it defaults to the value of the first <Format> in <GetMap> in the GetCapabilities response.

Indicates the maximum height of the image exported by the service.

Indicates the maximum width of the image exported by the service.

Indicates whether the background of the image exported by the service is transparent.

Indicates whether the layer will be included in the legend.

The maximum scale (most zoomed in) at which the layer is visible in the view. If the map is zoomed in beyond this scale, the layer will not be visible. A value of 0 means the layer does not have a maximum scale. The maxScale value should always be smaller than the minScale value, and greater than or equal to the service specification.

The minimum scale (most zoomed out) at which the layer is visible in the view. If the map is zoomed out beyond this scale, the layer will not be visible. A value of 0 means the layer does not have a minimum scale. The minScale value should always be larger than the maxScale value, and lesser than or equal to the service specification.

Enable persistence of the layer in a WebMap or WebScene.

The portal item from which the layer is loaded. If the portal item references a Feature Service or Scene Service, then you can specify a single layer to load with the layerId property.

Refresh interval of the layer in minutes. Value of 0 indicates no refresh.

The spatial reference of the layer.

List of spatialReference well known ids derived from the CRS elements of the first layer in the GetCapabilities request.

A subset of the layer's WMSSublayers that will be displayed.

If you set the sublayers property at the time of the layer's initialization, this will override the sublayer information from the service. For example, if you define a sublayer at layer initialization based on the name, as shown in the snippet below, other sublayer properties, such as the legendUrl, minScale, and maxScale, will be set to the default values from the API, not the values defined in the service.

const wmsLayer = new WMSLayer({
  url: "url-to-wms-service",
  sublayers: [{
    name: "sublayer-name"
  }]
});

Alternatively, in order to retain the service's definition for each sublayer, update the sublayers property after loading the layer as demonstrated below.

const wmsLayer = new WMSLayer({
  url: "url-to-wms-service"
});
await wmsLayer.load();
const sublayer = wmsLayer.findSublayerByName("sublayer-name");
if (sublayer) {
  wmsLayer.sublayers = [sublayer];
}

The layer's time extent. When the layer's useViewTime is false, the layer instructs the view to show data from the layer based on this time extent. If the useViewTime is true, and both layer and view time extents are set, then features that fall within the intersection of the view and layer time extents will be displayed. For example, if the layer's time extent is set to display features between 1970 and 1975 and the view has a time extent set to 1972-1980, the effective time on the feature layer will be 1972-1975.

TimeInfo provides information such as date fields that store start and end time for each feature and the fullTimeExtent for the layer. The timeInfo property is automatically set at layer initialization if the layer has one or more time dimensions. The fullTimeExtent for timeInfo is automatically set to the union of all time dimension extents. The timeInfo parameters cannot be changed after the layer is loaded.

A temporary offset of the time data based on a certain TimeInterval. This allows users to overlay features from two or more time-aware layers with different time extents. For example, if a layer has data recorded for the year 1970, an offset value of 2 years would temporarily shift the data to 1972. You can then overlay this data with data recorded in 1972. A time offset can be used for display purposes only. The query and selection are not affected by the offset.

The title of the layer used to identify it in places such as the Legend and LayerList widgets.

When the layer is loaded from a portal item, the title of the portal item will be used. If a layer is loaded as part of a webmap or a webscene, then the title of the layer as stored in the webmap/webscene will be used.

The URL of the WMS service.

Determines if the layer will update its temporal data based on the view's timeExtent. When false, the layer will display its temporal data based on the layer's timeExtent, regardless of changes to the view. If both view and layer time extents are set while this property is true, then the features that fall within the intersection of the view and layer time extents will be displayed. For example, if a layer's time extent is set to display features between 1970 and 1975 and the view has a time extent set to 1972-1980, the effective time on the feature layer will be 1972-1975.

Version of the WMS specification to use. For example, 1.3.0, 1.1.1, 1.1 or 1.0.