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I think this issue is caused by same limitation of heatmap implementation which I described in question mentioned by Andrew. For now heatmap is rendered as single texture which has size of the data series ( in your case it has size 116×50 pixels ). Width of chart is 200 pixels minus width of yAxis which I would say takes ~20% of chart’s width on your screenshot. So let’s say that width of heatmap is ~160 pixels. This means that for each texture pixel we have 1.38 device pixels and on real device you can’t render such amount of pixel for obvious reasons ( you can set red color for 1 or 2 pixels but you can’t set it for half of the pixel ). So in this case depending on coordinate of texture pixels OpenGL rasterizer in one case sets 1 pixel (e.g. case when texture pixel should be drawn from 1 to 2.38 pixel it will be rounded and drawn from 1 to 2 pixel ) and in other sets 2 pixels to be red ( e.g. case when texture pixel should be drawn from 1.2 to 2.58 device pixels which after rounding to closest value will become 1 to 3 ). That’s why you see different line thickness. Unfortunately there is nothing we can do to improve this situation without rewriting heatmap to draw each device pixel on our own instead of leaving interpolation of heatmap texture pixel values to OpenGL.