While we are having this discussion, I would like to mention a little thing which always bothers me about the use of the word centroid in this context.

The word centroid has a specific meaning in GIS terms, that is a point, the coordinates of which are calculated from the geography of a GI object (or usually polygon). I imagine there are a number of ways this can be done and probably different GIS softwares use different methods, but basically it is an average of the node positions.

So far so good, but that implies a couple of things; firstly that there is only one centroid for a given polygon and software/methodology and secondly, that the centroid may not always lie within the polygon (where the polygon includes holes or the boundary is partially concave).

Obviously it is not desirable to have a spatial reference associated with a Location which is outside the location boundary, particularly when doing spatial queries. There is enough room for error in reducing a site-based record down to a six-figure grid reference without using a grid reference which isn't even in the right area/habitat or whatever. It is of course normal practice to assign a grid reference to a location by picking a suitable location (within the location boundary) from the map, but the temptation may be there to just let the GIS generate a centroid without checking.

All of this should be obvious to anyone who has spent any time handling GI biodiversity data, but it is also something which I often have to point out to less experienced users and the fact that Recorder uses Site Centroid as one of the spatial reference types (and doesn't offer a more appropriate term) doesn't help.

So my point is that when we talk about the grid reference associated with a Location in Recorder, it is better not to call it a centroid. It is in fact a nominal site grid reference.

Just a little personal niggle really, but I feel better now I have got it off my chest.