es x-coordinates and y-coordinates of the design sites.
When the analysis data is an <code>sf</code> object, the coordinates
from the data’s geometry are used. When the analysis data is just a data
frame, x-coordinates and y-coordinates (from an appropriate coordinate
reference system) must be provided using the <code>xcoord</code> and
<code>ycoord</code> arguments, respectively, of the analysis function
being used.</p>
<p>Several additional variance estimation options are available in
spsurvey’s analys