The sLap slider lets you set the "distance round track" range to zoom in to data traces from different parts of the track.
Note: the data shows sensor samples vs distance round the track collected over the whole of the race. If Hamilton did exactly the same line for each tour, the GPS points vs distance should match... Becuase the data is collected from multiple laps, it is possible for several different values to be displayed for any given sLap value.
For a way of visuliasing the data across the whole race on a per lap basis, see eg F1 Data Junkie – Driver DNA
Peeking at some of the examples, it should be possible to add in a drop down list that allows you to set the sLap range from the turn number (assuming you map the sLap range to corner number before hand...?