Hectad

Those taxa that show interesting distributions have been mapped and included here, their maps incorporating earlier records made by Laflin and others from 1958 to 1968 which had been based only on localities with hectad grid references.

This comprises the proportion of each hectad covered by each of ten land-cover types: sea, coastal, arable, broadleaf forest, built-up, conifer forest, improved grassland, open water (rivers, lochs, etc.), semi-natural and upland. The temperature used was taken to be the annual temperature per hectad averaged over the period 1920–1999 […]

They took figures for the abundance of invasive weeds mapped according to the normal grid unit of the 'hectad', or 10 × 10 km square, and then looked at how abundant these species were mapped at a much finer scale – in 'tetrads', or 2 × 2 km squares, inside these hectads.

Certainly pampas grass made a slow start in the wild in this country [United Kingdom]; despite being grown here since 1848, it was recorded in only 21 hectads (10 x 10km squares) up to 1986, but is now recorded in 425.