I've just starting using vega and when I use this code:

{
  "$schema": ".json",
  "height": 300,
  "widht": 400,
  "title": "The London boroughs",
  "layer": [
    {
      "data": {
        "url": ".github.io/refs/heads/main/ldn_boroughs.geojson"
      },
      "mark": {
        "type": "geoshape",
        "fill":"lightgray",
        "stroke": "black",
        "strokeWidth": 0.4
      }
    },
  ]
}

I see a square: vega lite

I was hoping to see the map, but I didn't. I am really confused as to why it's happening since it works with other geoJson files. Any thoughts? Thanks so much