strikesByAirport = d3.groups(laserStrikes, d => d.Airport)
.map(d => {
return {
airport: d[0],
strikes: d[1].length,
traffic: d[0] in usAirports ? usAirports[d[0]].Enplanements : 0,
name: d[0] in usAirports ? usAirports[d[0]].Airport : ''
}
}).filter(d => d.traffic > 0)