Unfortunately there is not really a way around this without having a huge network of servers everywhere. The ping is from Quebec so it will differ based on where shards are. On the shard listing page it mentions this at the bottom.
The graph provides a good idea of overall stability, if the ping is constant it's good, if there are spikes it could mean a shard issue.
One thing I could possibly do at some point is rather than show the actual ping, I could keep a running average then show some kind of value that indicates if it's far or close to average.