Using the API you can get both the Segment altitude data and the Segment Effort altitude data. The segment data is what's displayed on the website and can be bad. But the Segment Effort data would be a subset of the data from the activity. So you can get many many versions of the altitude for the segment and do any type of analysis you wish.
The overlay tiles zoom weird in leaflet. They get treated like a base layer so when you zoom, they get scaled 2x and the new tiles load on top. That doesn't look right when the tiles are transparent. There must be an option to fix this but couldn't find it.
I couldn't get the styles I wanted with mapbox so I just defaulted to google.
On this map I took out any point within 1km of the start or end of every ride. This is stronger than what users have set and eliminates 1000s of "hot spot".
I've looked into a couple of these cases and it's friends "coming by for a ride" or them stopping at their house mid ride.
I'm working on further eliminating these points by just not included "stopped" points. I've also tried doing some image processing to remove these hot spots but have had mixed results.
Each pixel has a count. Each tile gets a 90 percentile value. Every corner gets the average of its 4 tiles. Every pixel in the currently requested tile gets a value [0, 1] based on the bi-linearly interpolated "max". It's then colored based on that final value.