ll be done spatially in a first step, and then:
if <code>(spillOver = "unique")</code> assigns (and moves) all observations with same visitUID
to the grid cell with most observations (or picks one grid cell at random if
there is a tie); or if <code>(spillOver = "duplicate")</code> duplicates all
observations with same visitUID across all grid cells containing at least one
observation with that visitUID.</p>
<p>The later approach is useful when the amount of observations spilled over
neighbouring cells is mi