Why does HeatSeries.PointPadding(0) cause a 1px border and HeatSeries.PointPadding(-1) cause no border?

[begleysm]

I am working on creating a Range Doppler map (basically a HeatSeries forming a 2D graph of measured amplitudes with Range & Doppler bins on the Y & X axes respectively).

They typically look something like this

I was surprised to find that HeatSeries.PointPadding = new Padding(0) produces little (1px?) borders like this

and that I had to try HeatSeries.PointPadding = new Padding(-1) to get rid of it and have the cells actually seamlessly "touch" one another.

Is there a better way to do this? Like to disable a border or something? I couldn't find anything that seemed better in the API