Unable to combine legends when using line mark with "point": true or separate line and point layers #9748

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1. labkey-alan

   added

   Bug 🐛

   on Jan 9, 2026
2. labkey-alan commented on Jan 9, 2026

   

   labkey-alan

   on Jan 9, 2026

   Last edited by labkey-alan

   Author

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   Here is another visualization that I created that shows the same problem, but with a slightly different Vega-Lite spec. Here is the spec without the data (the link to the Vega Editor includes the data):

   {
     "$schema": "https://vega.github.io/schema/vega-lite/v6.json",
     "data": {
       "values": []
     },
     "layer": [
       {
         "mark": {"type": "line", "point": false},
         "encoding": {
           "color": {"field": "type.value", "type": "nominal", "title": "Type"}
         }
       },
       {
         "mark": {"type": "point", "opacity": 1, "filled": true, "size": 55},
         "encoding": {
           "color": {"field": "type.value", "type": "nominal", "title": "Type"},
           "shape": {"field": "type.value", "type": "nominal", "title": "Type"}
         }
       }
     ],
     "encoding": {
       "x": {
         "field": "maxSpeed.value",
         "type": "quantitative",
         "title": "Max Speed"
       },
       "y": {"field": "weight.value", "type": "quantitative", "title": "Weight"}
     }
   }

   So, instead of trying to use just the line mark with "point": true I went ahead and created two individual layers, one for the lines, one for the points. Each layer defines their own color encoding, and the point layer includes an encoding for shape. I would expect this to result in a combined legend, but it does not. The results are basically identical to using only the line mark with "point": true. I tried disabling the legend for the line layer but that just drops the color values from the legend.

   
3. labkey-alan

   changed the title [-]Using mark type line with point: true does not combine legends[/-] [+]Unable to combine legends when using line mark with "point": true or separate line and point layers[/+] on Jan 9, 2026
4. ByzantineFailure commented on Mar 19, 2026

   

   ByzantineFailure

   on Mar 19, 2026

   Last edited by ByzantineFailure

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   Noting that we encounter this issue as well when attempting to use a shape mark to apply symbols to different series in a stacked bar chart for accessibility purposes (need a non-color way to differentiate them).

   {
     "$schema": "https://vega.github.io/schema/vega-lite/v5.json",
     "description": "A simple bar chart with embedded data and shapes in the center",
     "data": {
       "values": [...],
     },
     "transform": [
       {
         "stack": "b",
         "groupby": ["a"],
         "as": ["y0", "y1"]
       },
       {"calculate": "(datum.y0 + datum.y1) / 2", "as": "midpoint"}
     ],
     "encoding": {
       "x": {"field": "a", "title": "Category", "type": "nominal", "axis": {"labelAngle": 0}},
       "color": {
         "field": "c",
         "title": "Product",
         "type": "nominal",
         "scale": {"scheme": "category20"}
       },
       "shape": {
         "field": "c",
         "type": "nominal"
       }
     },
     "layer": [
       {
         "mark": {"type": "bar"},
         "encoding": {
           "y": {"field": "y0", "type": "quantitative", "title": "Value" },
           "y2": {"field": "y1", "title": "Value", "type": "quantitative"},
         }
       },
       {
         "mark": {"type": "point", "filled": true, "stroke": "black", "size": 100},
         "encoding": {
           "y": {"field": "midpoint", "type": "quantitative"},
         }
       }
     ]
   }