LayerDescription

Base Type: MapTableDescription

A class that describes the contents of a layer in a map service.

Property	Type	Description
DefinitionExpression	string	A where clause used to filter features for some query and display operations.
DrawingDescription	LayerDrawingDescription	Defines how a layer will be symbolized
LayerID	int	The unique id of the layer.
LayerResultOptions	LayerResultOptions	Defines if and how geometry is included in query results.
ScaleSymbols	bool	Indicates whether the layer should scale symbols according to a reference scale set in the default map (default map description).
SelectionBufferDistance	double	The buffer distance around selected features. It is defined in map units.
SelectionBufferSymbol	FillSymbol	The symbol of the buffer.
SelectionColor	Color	The color of selected features in a layer.
SelectionFeatures	int[]	An array of Feature IDs (FIDs) to render as selected features.
SelectionSymbol	Symbol	The symbol of selected features.
SetSelectionSymbol	bool	Indicates if should override default selection symbol.
ShowLabels	bool	If a layer has labels, define if they should be displayed in a map.
ShowSelectionBuffer	bool	If a selection buffer is defined (SelectionBufferDistance), show the buffer using the SelectionBufferSymbol.
Source	MapServerSourceDescription	Defines the data source for a dynamically added table or layer
SourceID	string	The id of results from a geoprocessing job (same as the job id). Used to define the source for a tool layer in a map service.
TimeDataCumulative	bool	Indicates if features will be animated cumulatively.
TimeDataCumulativeSpecified	bool	Indicates if TimeDataCumulative is specified.
TimeOffset	double	The time offset that needs to be applied to the data for drawing.
TimeOffsetSpecified	bool	Indicates if TimeOffset is specified.
TimeOffsetUnits	esriTimeUnits	The recommended time interval units to be used to animate this layer/ table.
TimeOffsetUnitsSpecified	bool	Indicates if TimeOffsetUnits is specified.
UseTime	bool	Indicates whether or not a layer should use the TimeSpan in the MapDescription to draw its contents.
UseTimeSpecified	bool	Indicates if UseTime is specified.
Visible	bool	Indicates if the layer is visible in a map.

Remarks

This object can be used to modify the presentation and use of a layer in a map. For example, you can use it to turn layers on/off when generating a map image or limit a query by applying a layer definition. These settings include a unique ID for the layer (LayerID), an ID the corresponds with a Geoprocessing job (SourceID), a boolean indicating if the layer is visible as defined in the table of contents, i.e. the layer is marked on (Visible), a boolean to indicate whether the layer should display its dynamic labels (ShowLabels) if labels for this layer are available to the map service, a boolean to indicate whether the layer should scale it symbols according to a reference scale set in the map (ScaleSymbols).

SourceID is used for map service interaction with the Geoprocessing server. It is a unique job id assigned to a geoprocessing service each time it runs on the server. This property can be used to find out which geoprocessing job has created this layer. It is important to note that LayerID, SourceID and the index of layers in map document are not the same.

In order for symbols to scale, the map must have a reference scale set and the layer must support symbol scaling. Use ScaleSymbols to activate or deactivate a layer's symbol scaling. If a map does not have a set reference scale setting, ScaleSymbols will have no effect. Use CanScaleSymbols on MapLayerInfo to verify if a layer supports symbol scaling. A reference scale is set within the original map document.

Not all map service layers have available labels. To see if the layer has labels use HasLabels on MapLayerInfo.

DefinitionExpression:

The LayerDescription includes a DefinitionExpression. A DefinitionExpression can be set on a layer in order to limit layer features available for display or query. This only applies for the request and does not replace the definition query set in the source map.

When UseStandardizedQueries is True:

• the DefintionExpression of a LayerDescription retrieved from MapServerInfo.DefaultMapDescription is always empty regardless of whether a definition expression is set on the layer in the source map.
• an expression set in the LayerDescription will be appened to the one set for the layer in the source map.
• you can only use StandardizedQueries. This means you will always format a query on a date field the same way or if you want to find all features where the value in a string field contains a specified keyword, you can use the same function name regardless of the underlying database type. Queries containing anything specific to the underlying database, for example, a function that is only supported by the database but is not part of the StandardizedQueries specification will fail.

When UseStandardizedQueries is False:

• a layer can have a default definition expression that is set for that layer in the source map.
• an expression set in the LayerDescription will override the one set for the layer in the source map.
• the query must conform to the underlying database's syntax and use functions supported by that database.

Let's look at some examples. Queries mentioned in these examples can be used regardless of the value of UseStandardizedQueries.

You have a layer in your map that represents sales regions. The layer includes fields: REGIONS, SALES and MANAGER.

• Example #1: In the source map the layer has a definition query, "REGION = 'North'". No DefintionExpression is specified in LayerDescription. Only those features where REGION = 'North' will be displayed in your map.

• Example #2: In the source map the layer has a definition query, "REGION = 'North'". You apply a DefinitionExpression in LayerDescription as "SALES > 1000". The LayerDescription DefinitionExpression overrides the definition query set in the source map. Only those features where SALES > 1000 will be displayed in your map.

  If you wish to use the DefinitionExpression as a way of getting a subset of the features already filtered by the definition query in the map you will need to save the original expression and then add it to the new expression to form one compound expression, REGION = 'North' AND SALES > 1000. This will display map features that are belong to the North region and have sales over 1000.

• Example #3: In the source map the layer has no definition query. You apply a DefinitionExpression in LayerDescription as "SALES > 1000". Only those features where SALES > 1000 will be displayed in your map.

The following MapServer methods will honor DefinitionExpression: Find, Identify, QueryFeatureCount2, QueryFeatureIds2, QueryFeatureData2. The following map service methods will only use the definition expression set in the source map since a MapDescription or LayerDescription is not provided as a parameter: QueryFeatureCount, QueryFeatureIds, and QueryFeatureData. Note that DefinitionExpression does not affect spatial extents.

Please note that the following properties only honored in ExportMapImage and Identify operations:

• UseTime
• TimeDataCumulative
• TimeOffset TimeOffsetUnits

Examples

C#

//Example #1: set a simple render to a layer (assuming you have variables i.e. pMapServer, pMapDescription, pLayerDescription and pImageDescription are referenced correctly)

//symbol for polygon outline
RgbColor pGreyColor = new RgbColor()
{
	Red = 110,
	Green = 110,
	Blue = 110
};

SimpleLineSymbol pOutline = new SimpleLineSymbol()
{
	Style = esriSimpleLineStyle.esriSLSSolid,
	Width = 1,
	Color = pGreyColor
};

//Solid fill symbol with red fill color
RgbColor pRedColor = new RgbColor();
pRedColor.Red = 255;

SimpleFillSymbol pSimpleFillSymbol = new SimpleFillSymbol()
{
	Style = esriSimpleFillStyle.esriSFSSolid,
	Color = pRedColor,
	Outline = pOutline
};

SimpleRenderer pSimpleRenderer = new SimpleRenderer();
pSimpleRenderer.Symbol = pSimpleFillSymbol;
pSimpleRenderer.Label = "Rivers";

//setting LayerDrawingDescription 
FeatureLayerDrawingDescription pFLDD = new FeatureLayerDrawingDescription();
pFLDD.FeatureRenderer = pSimpleRenderer;

pLayerDescription.DrawingDescription = pFLDD;
MapImage pMapImage = pMapServer.ExportMapImage(pMapDescription, pImageDescription);

//Example #2: changing only the DefaultSymbol for a layer (assuming you have variables i.e. pMapServer, pMapDescription, pLayerDescription, pImageDescription and strCurrentMapName are referenced correctly)

//symbol for polygon outline
RgbColor pGreyColor = new RgbColor()
{
	Red = 110,
	Green = 110,
	Blue = 110
};

SimpleLineSymbol pOutline = new SimpleLineSymbol()
{
	Style = esriSimpleLineStyle.esriSLSSolid,
	Width = 1,
	Color = pGreyColor
};

//Solid fill symbol with red fill color
RgbColor pRedColor = new RgbColor();
pRedColor.Red = 255;

SimpleFillSymbol pSimpleFillSymbol = new SimpleFillSymbol()
{
	Style = esriSimpleFillStyle.esriSFSSolid,
	Color = pRedColor,
	Outline = pOutline
};

//getting the default drawing description of the first layer
int[] pLyrIDs = new int[]{intLayerID};
LayerDrawingDescription[] pLDDs = pMapServer.GetDefaultLayerDrawingDescriptions(strDefaultMapName, pLyrIDs, null);
FeatureLayerDrawingDescription pFlyrDD = pLDDs[0] as FeatureLayerDrawingDescription;

//getting the renderer and changing the defaultSymbol to solid fill with red color
UniqueValueRenderer pUVR = pFlyrDD.FeatureRenderer as UniqueValueRenderer;
pUVR.DefaultSymbol = pSimpleFillSymbol;

//setting the renderer and changing the defaultSymbol to solid fill with red color
pLayerDescription.DrawingDescription = pFlyrDD;
MapImage pMapImage = pMapServer.ExportMapImage(pMapDescription, pImageDescription);