ference/sf.html" class="external-link">sf::sf()</a></code> object containing the solution also contains additional
columns, then these columns will need to be subsetted prior to using this
function (see below for example).
Additionally, the argument to <code>solution</code> must also have the same
coordinate reference system as the planning unit data.
Furthermore, any planning units missing cost
(<code>NA</code>) values for a particular zone should also have missing (<code>NA</code>)
values in the argument 