I am working on the Map Data Across The Globe project, but I am having trouble sizing the circles that represent where the meteorites have fallen.

Specifically, can you set the path.pointRadius with a function? If so, how. this is what I have tried:

```
var projection = d3.geoMercator()
.center([8, 0 ])
.scale(100)
.rotate([0,0]);
var path = d3.geoPath().projection(projection);
svg.append("path")
.datum(meteoriteData)
.attr("d", path)
.attr('d', (d) => path.pointRadius(d.r));
```

Thanks