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One common style for density plots is to have a vertical legend that is the same height as the plot itself. Some example density plots from Google Image search:

Density plots from Google Image search

How can we make DensityPlots with legends whose height matches the height of the plot? By default the heights are different:

DensityPlot[Sin[x] Sin[y], {x, -4, 4}, {y, -3, 3}, 
 PlotLegends -> Automatic]

Default DensityPlot with legend

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2  
I guess you mean with the new built-in legending? If not, there's this –  rm -rf Nov 28 '12 at 23:04
2  
You can resize them manually. They have handles you can drag. –  Sjoerd C. de Vries Nov 28 '12 at 23:07
    
Maybe you can also use this –  Jens Nov 28 '12 at 23:12
    
It is odd that it clips the top of the frame, just did it on my machine and I get the same image artifact ... ugh –  Gabriel Nov 29 '12 at 0:37
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5 Answers

Elaborating a little on Sjoerd's answer:

Specifying LegendMargins makes it even clearer that the fancy new legend might be not as useful as I first thought. We now have a working legend but lost basically all control over its apearance:

DensityPlot[Sin[x] Sin[y], {x, -4, 4}, {y, -3, 3}, 
 ImageSize -> {300, 300},
 ImagePadding -> {{30, 30}, {30, 30}}, Background -> LightGray, 
 PlotLegends -> 
 BarLegend["LakeColors", 
           LegendMargins -> {{10, 0}, {30, 20}}, 
           LegendFunction -> (Framed[#, FrameMargins -> 10] &)
           ]]

enter image description here

The upper edge of the BarLegend appears to allign roughly with the Plot canvas, but we now have the additional 30 points Margin at the top. Unfortunately if we change the Bottom Margin everything rescales:

DensityPlot[Sin[x] Sin[y], {x, -4, 4}, {y, -3, 3}, 
 ImageSize -> {300, 300},
 ImagePadding -> {{30, 30}, {30, 30}}, Background -> LightGray, 
 PlotLegends -> 
  BarLegend["LakeColors", 
            LegendMargins -> {{10, 0}, {10, 20}}, 
            LegendFunction -> (Framed[#, FrameMargins -> 10] &)
           ]]

enter image description here

Again the Legend claims additional space above and below the Plot. Imagine the nightmare in a GraphicsGrid with different kinds of Plots. To me, it appears as if the chance of ever aligning to Plots (and their Legends) next to each other are basically zero.

Looking at the InputForm of the above Plot gives a huge expression with Head Legended:

Legended[ .......,
{Placed[BarLegend["LakeColors", LegendFunction -> (Framed[#1, FrameMargins -> 10] & ), LegendLayout -> "Column", LegendMargins -> {{10, 0}, {10, 20}}, LegendMarkerSize -> 300, Charting`TickSide -> Right, ColorFunctionScaling -> True, LegendMargins -> {{10, 0}, {10, 20}},
LegendFunction -> (Framed[#1, FrameMargins -> 10] & )] , After, Identity]}]

We note two things: first there is the use of LegendMarkerSize that appears to take the vertical ImageSize. Fiddling with it can improve the result a little:

DensityPlot[Sin[x] Sin[y], {x, -4, 4}, {y, -3, 3}, 
 ImageSize -> {300, 300},
 ImagePadding -> {{30, 30}, {30, 30}}, Background -> LightGray, 
 PlotLegends -> 
  BarLegend["LakeColors", 
  LegendMargins -> {{10, 0}, {-10, -10}}, 
  LegendFunction -> (Framed[#, FrameMargins -> 10] &), 
  LegendMarkerSize -> 300]
 ]

gives:

enter image description here

The second thing is the usage of ChartingTickSide -> Right`, which controls where the Ticks are written.

I tried to find where the Charting*` stuff is defined, but could only get the following large list of expressions:

Names["Charting`*"]

{"Charting'angleCalc", "Charting'angleToValue", 
 "Charting'AngularScale", "Charting'apportion", 
 "Charting'AutomaticBar", "Charting'AutomaticBar3D", 
 "Charting'AutomaticBubble", "Charting'AutomaticBubble3D", 
 "Charting'AutomaticSector", "Charting'AutomaticSector3D", 
 "Charting'AutomaticTrap", "Charting'AxesLabelRotate", 
 "Charting'AxisAnnotation", "Charting'AxisAppearance", 
 "Charting'AxisFactor", "Charting'AxisLabel", "Charting'BackTesting", 
 "Charting'barPointtoValue", "Charting'barValHeight", 
 "Charting'barValueToPoint", "Charting'BoxElements", 
 "Charting'BulletCheck", "Charting'canonicalPlotLegends", 
 "Charting'canonicalWrapperLegends", "Charting'CanvasPadding", 
 "Charting'CategoricalAxis", "Charting'CategoryBounds", 
 "Charting'CategorySpacing", "Charting'ChartArgCheck", 
 "Charting'ChartHighlighting", "Charting'ChartLegendsParser", 
 "Charting'ChartParser", "Charting'ChartStyleBlock", 
 "Charting'ChartStyleInformation", "Charting'checkChartElement", 
 "Charting'checkColor", "Charting'checkGridLines", 
 "Charting'ClickEffect", "Charting'ClockCheck", 
 "Charting'colorfunctionScale", "Charting'CompleteSizes", 
 "Charting'computeScenePlotRange", "Charting'computeSceneRange", 
 "Charting'ConstructColorFunction", "Charting'ConstructDirective", 
 "Charting'ConstructErrorBars", "Charting'constructLegends", 
 "Charting'CoordinateListQ", "Charting'CoordinateQ", 
 "Charting'createDefaultLabels", "Charting'createPlotRange", 
 "Charting'createPlotRange3D", "Charting'dataExtremes", 
 "Charting'DateAxis", "Charting'datedDataExtremes", 
 "Charting'DateFormat", "Charting'DateScale", "Charting'DateScope", 
 "Charting'DateValueParser", "Charting'dbPrint", 
 "Charting'DefaultPlotStyle", "Charting'DisplayFunctionTest", 
 "Charting'DivisionLabelingFunction", "Charting'drawLegendMarkers", 
 "Charting'drawLegends", "Charting'drawMarkers", 
 "Charting'drawMarkers3D", "Charting'DynamicAction", 
 "Charting'DynamicImage", "Charting'edgeDirective", 
 "Charting'emptyDataQ", "Charting'ErrorBar", 
 "Charting'ErrorBarFunction", "Charting'ErrorBarSize", 
 "Charting'ErrorBarStyle", "Charting'expandFilling", 
 "Charting'expandPlaced", "Charting'expandPlotRange", 
 "Charting'expandPlotRange3D", "Charting'extractLabels", 
 "Charting'FilterGraphics3DOptions", "Charting'FilterGraphicsOptions", 
 "Charting'FinancialIndicatorList", 
 "Charting'FinancialIndicatorLists", "Charting'FinancialIndicators", 
 "Charting'FinancialPattern", "Charting'findAxesOrigin", 
 "Charting'FindGrid", "Charting'findPlotRange", "Charting'FindTicks", 
 "Charting'FindTicksP", "Charting'gaugeBoxes", "Charting'GaugeCheck", 
 "Charting'generalDirective", 
 "Charting'generateLegendDynamicVariable", "Charting'generateLegends", 
 "Charting'get2DPlotRange", "Charting'get3DPlotRange", 
 "Charting'getBasicStyles", "Charting'getBasicStyles2", 
 "Charting'getDataExtremes", "Charting'getExtremes", 
 "Charting'GetGraphicsOptions", "Charting'getPlotStyles", 
 "Charting'getQuantityLabel", "Charting'getSideMarker", 
 "Charting'getTargetUnits", "Charting'getTrendStyle", 
 "Charting'gridlinesFinder", "Charting'HeldOptionQ", 
 "Charting'Highlighted", "Charting'HistArgCheck", 
 "Charting'HorizontalScale", "Charting'iBarChart", 
 "Charting'iBarChart3D", "Charting'iBarLegend", 
 "Charting'iBoxWhiskerChart", "Charting'iBubbleChart", 
 "Charting'iBubbleChart3D", "Charting'iCandlestickChart", 
 "Charting'iDensityHistogram", "Charting'iDialGauge", 
 "Charting'iDistributionChart", "Charting'iFinancialIndicatorLists", 
 "Charting'iHistogram", "Charting'iHistogram3D", 
 "Charting'iHistogramList", "Charting'iInteractiveTradingChart", 
 "Charting'iKagiChart", "Charting'iLegended", "Charting'iLinearGauge", 
 "Charting'iLineBreakChart", "Charting'iLineLegend", 
 "Charting'IndicatorFunction", "Charting'Indicators", 
 "Charting'interactiveTradingChartActionMenu", 
 "Charting'interactiveTradingChartResetButton", 
 "Charting'interactiveTradingChartSnapshotButton", 
 "Charting'iPairedBarChart", "Charting'iPairedHistogram", 
 "Charting'iPointFigureChart", "Charting'iPointLegend", 
 "Charting'iRenkoChart", "Charting'iSectorChart", 
 "Charting'iSectorChart3D", "Charting'iSwatchLegend", 
 "Charting'iTradingChart", "Charting'LabelSide", "Charting'Legend", 
 "Charting'LegendCanvas", "Charting'LegendConstructer", 
 "Charting'legendize", "Charting'LegendSize", 
 "Charting'LegendWrapper", "Charting'listDepthCount", 
 "Charting'ListScale", "Charting'lookUpIndicators", 
 "Charting'mainChart", "Charting'makeDynamicModule", 
 "Charting'makeGaugeBoxes", "Charting'MemoryLeakTest", 
 "Charting'MouseEffect", "Charting'nearestDate", "Charting'negativeQ", 
 "Charting'nonNegativeQ", "Charting'noShow", "Charting'Nothing", 
 "Charting'OHLC", "Charting'OHLCV", "Charting'optCheck", 
 "Charting'padChartElements", "Charting'PadLabels", 
 "Charting'padList", "Charting'padMarkerStyle", 
 "Charting'padMarkerStyle2", "Charting'padMarkerStyle3", 
 "Charting'PairedCategoryAxis", "Charting'PairedChartArgCheck", 
 "Charting'PairedHistArgCheck", "Charting'ParametricScale", 
 "Charting'parseBulletChart", "Charting'parseChartElements", 
 "Charting'parseChartElementsRow", "Charting'parseChartLabels", 
 "Charting'parseChartLabelsRow", "Charting'parseChartLegends", 
 "Charting'parseChartLegends2", "Charting'parseClock", 
 "Charting'parseLabelingFunction", "Charting'parseLegendPlotStyle", 
 "Charting'parsePlotMarkers", "Charting'parsePlotMarkers3D", 
 "Charting'parseThermometer", "Charting'PatternsFunction", 
 "Charting'PFLP", "Charting'PictorialBar", "Charting'PictorialBar3D", 
 "Charting'PictorialBubble", "Charting'PictorialBubble3D", 
 "Charting'PictorialTrap", "Charting'PlainAutomaticBar3D", 
 "Charting'PlotArgCheck", "Charting'PlotOrigin", 
 "Charting'PlotParser", "Charting'PlotTheme", 
 "Charting'polarMarkerLabeling", "Charting'polarMarkerLabeling3D", 
 "Charting'polygonDirective", "Charting'positiveQ", 
 "Charting'PruneOptions", "Charting'RadialScale", 
 "Charting'RangeBarChart", "Charting'realNumericQ", 
 "Charting'RenderAssembler", "Charting'RenderMarker", 
 "Charting'RenderMouseEffect", "Charting'rescale", 
 "Charting'resetAngle", "Charting'resolveHighlighting", 
 "Charting'resolveLabeled", "Charting'resolveLabeledDynamic", 
 "Charting'resolveLabeledStatic", "Charting'resolveLabelingFunction", 
 "Charting'resolveLabelingFunctionDynamic", 
 "Charting'resolveLabelingFunctionStatic", 
 "Charting'resolveMarkerLabeling", "Charting'resolvePlaced", 
 "Charting'resolvePlacedDynamic", "Charting'resolvePlacedStatic", 
 "Charting'resolvePlotRangePadding", "Charting'ResolvePlotTheme", 
 "Charting'RotateLabels", "Charting'RotateTicks", "Charting's", 
 "Charting'safeColor", "Charting'ScaleAxes", "Charting'ScaleAxis", 
 "Charting'ScaleAxis3D", "Charting'ScaledFrameTicks", 
 "Charting'ScaledTicks", "Charting'ScaledTicks2", 
 "Charting'ScaledTickValues", "Charting'scaledValues", 
 "Charting'scientificForm", "Charting'SetChartStyleInformation", 
 "Charting'SimplePadding", "Charting'StudiesFunction", 
 "Charting'styleTree", "Charting's$", "Charting'TickAnnotations", 
     "Charting'TickLabels", "Charting'TickLengths", 
     "Charting'TickMarkers", "Charting'TickSide", "Charting'TickWrappers", 
     "Charting'TimeAxis", "Charting'TimelineParser", "Charting'TimeScale", 
     "Charting'tradingChartGridlinesFinder", 
     "Charting'TradingChartIndicator", "Charting'TradingChartSlider", 
     "Charting'Tukey5", "Charting'Tweaked", "Charting'unitConverting", 
     "Charting'UnsetChartStyleInformation", "Charting'value2pts", 
     "Charting'valueToAngle", "Charting'varCheck", 
     "Charting'VerticalScale", "Charting'$Graphics3DExtraOptions", 
 "Charting'$GraphicsExtraOptions", "Charting'$MajorTickLength", 
 "Charting'$MinorTickLength", "Charting'$PlotTheme", 
 "Charting'$PlotThemes"} 

So maybe there is some chance left to regain control over our plots. However, this is beyond me. Please, could somebody explain to me the reasoning behind the new Legended functionality and the Layout? What were they thinking??

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If you provide BarLegend as an explicit option value of PlotLegends it seems to do what you want:

DensityPlot[Sin[x] Sin[y], {x, -4, 4}, {y, -3, 3}, 
 ImageSize -> {300, 300}, PlotLegends -> BarLegend["LakeColors"]]

Mathematica graphics

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2  
almost... it's now offset vertically. –  rm -rf Nov 28 '12 at 23:15
10  
@rm-rf That will surely be fixed by version 18... –  Jens Nov 28 '12 at 23:28
    
@Jens I almost chocked on my noodles laughing ... –  Gabriel Nov 28 '12 at 23:54
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This makes me happy. Still a usage case for ye-olde-colorbarplot package :) I've not checked if it works in v9 though!

http://www.walkingrandomly.com/?p=2960

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I have tested tested colorplot package with v9 from walkingrandomly.com/?p=2960 everything works just fine, thanks. –  Tuku Nov 29 '12 at 15:50
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Hope this workaround helps.

Use Placed to position legends more precisely:

DensityPlot[Sin[x] Sin[y], {x, -4, 4}, {y, -3, 3}, 
 PlotLegends -> 
  Placed[BarLegend[Automatic, LegendMarkerSize -> 280], {1.05, 0.52}]]

enter image description here

{1.05, 0.52} is a scaled position referred to the DensityPlot.

The offset here, 0.52 instead of 0.5, is because frame tick labels move the plot off center. The same reasoning applies to the BarLegend itself sometimes because the tick labels can move the gradient off center (this example is lucky to have symmetric labels on both ends).

LegendMarkerSize->280 is because the DensityPlot has some plot range padding that needs compensation.

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Can you add more Details on how you obtained the values (0.02 offset, the 1.05and the 280)? –  Ronny Nov 29 '12 at 21:38
    
I guess those offsets are just hand chosen... but this is good to know anyway. This is a good option for one-off cases I think. –  Andrew Moylan Nov 29 '12 at 21:42
1  
I wonder if an Aligned[...] wrapper could be created, by analogy with Placed[...]. Aligned[expr, Top, tag] tries to align the Top of expr with other Aligned elements with the same tag. –  Andrew Moylan Nov 29 '12 at 21:43
    
@Andrew Right, it is difficult to get the number right programmatically because.. 1. PlotRangePadding is by default Scaled. 2. LabelStyle can also affect the ticks label size both in plots and BarLegend. –  MinHsuan Peng Nov 29 '12 at 21:44
1  
@Ronny, 1.05 means Scaled[1.05] refer to the plot. Scaled[{0,0}] is left bottom corner of the plot and Scaled[{1,1}] is right top corner. A double list give you full control. {pos_list, objpos_list} –  MinHsuan Peng Nov 29 '12 at 21:52
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In the featured example on changing legend orientations, they use the following:

PlotLegends -> Placed[BarLegend[Automatic, LegendLayout -> "Column"], After]

This appears to produce legends that align as wanted if accompanied by an explicit ImageSize. It still produces a slight vertical offset as in Sjoerd's answer.

As a side note, the four-plot combination on the same page is far from perfect because of the other misalignments.

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The options you mentioned seem - as far as i worked today with PlotLegends - to be the default values, hence they lead to exactely the image the OP postet. But Setting ImageSize -> 300 for the Plot will (why ever) do the Job on my PC (in contrary to @Sjoerd C.s answer), if I use only one Value and set the PlotRangePadding -> 0 –  Ronny Nov 29 '12 at 20:59
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