Markers in maps in iNaturalist are generally delivered as tiled image files, not actually as individual markers. This means that a user cannot directly interact with the markers displayed on the maps.
Instead, a user interacts with an invisible UTFgrid layer -- a grid of square cells -- that sits on top of the marker layer. The idea is that if a user interacts with a UTFgrid cell that is positioned on top of a particular marker, then the action triggered should correspond to an action meaningful for that marker.
The UTFgrid cells do not always approximate the shape of their corresponding markers correctly. This page provides a way to visualize the areas where an interaction can take place, alongside the corresponding markers that would be shown on an iNaturalist map.
A few notes:
First, this page uses a different set of basemaps than those available in iNaturalist (since the ones that iNaturalist uses are not free).
Second, I *think* the iNaturalist maps do some sort of fancy offset for the pin-style markers (the ones that look like upside down teardrops) so that their corresponding interaction areas are effectively shifted up a bit. (The effect would be that the corresponding interaction area in iNaturalist would be the fat end of a pin vs the narrow tip of a pin in this page.) Since this page does not do any fancy offsetting, you will just have to mentally do the shift to imagine where you would need to hover and click on an iNaturalist map.
Finally, the set of observations displayed by this page can be modified by adding parameters to the page URL. For example, if you would to see just bird observations by loarie, you could add "?user_id=loarie&taxon_id=3" to the end of the base URL. See the API reference for the Get Observations endpoint for a full list of parameters available to use.