longitude latitude channel makes the browser snap .. sometimes

[mattijn]

Originally reported at SO: https://stackoverflow.com/questions/79101599/how-to-solve-strange-plotting-error-in-altair

One of the weirdest bugs I've seen lately..

This specification gives a sad-face (Open the Chart in the Vega Editor):

{
  "$schema": "https://vega.github.io/schema/vega-lite/v5.20.1.json",
  "data": {"name": "ref"},
  "mark": {"type": "circle", "size": 500},
  "encoding": {
    "latitude": {"field": "lat", "type": "quantitative"},
    "longitude": {"field": "lon", "type": "quantitative"}
  },
  "datasets": {
    "ref": [
      {"lat": 51.4, "lon": 1.1},
      {"lat": 51.5, "lon": 1.2},
      {"lat": 51.31, "lon": 1.3},
      {"lat": null, "lon": null}
    ]
  }
}

When rounding the latitude value 51.31 to 51.3 there is no sad-face anymore, but only a very large white space (Open the Chart in the Vega Editor):

Removing the rows that contain null values can resolve the issue (Open the Chart in the Vega Editor):

Or by changing the latitude value 51.4 to a lower value like 51.2 and keep the null values in the dataset (Open the Chart in the Vega Editor):

But then there is again a strange white space area on the left. Weird, weird.

[PBI-David]

I see a few differences from what you observe.

Your first spec in Chrome with canvas render shows sad face. Switching to SVG render shows the dots.

Your first spec in FF with canvas render shows no sad face and just white space. Switching to SVG render shows the dots.