Add "site" tickmarks, or equivalent

[hyanwong]

Is it worth / possible to show the sites (perhaps just the variable ones?) as tickmarks on the top or the bottom (i.e. X axis) in the along-the-genome plots, such as the edge span plot? There are some regions which are quite data-sparse, so it might be useful to show that there are missing sites in these regions (or maybe that the sitres are all singletons or non-variable etc.).

We would have to think about if/how to do this when zoomed out, as there will be too many sites to show each one (in which case a site density plots might be better?)

[jeromekelleher]

It would be nice, but depends on technology.