Distribution
The distribution maps are dot maps of the region showing in which tetrads the species was found during cumulative fieldwork for the selected atlas. For breeding season atlases, the breeding status (present, possible, probable, confirmed) is indicated using differently sized dots. The numbers and percentage of tetrads of each breeding status category are shown in the left column.
Abundance
On the abundance maps, the average Timed Tetrad Visit (TTV) count data for each tetrad are presented by different densities of shading. The abundance category is calculated relative to the overall average hourly count for the species The numbers and percentage of tetrads in each abundance band are shown in the left column.
Distribution change
The distribution change maps show the differences in distribution between two atlas periods. Upward-pointing triangles show gains and improvements in breeding status, downward-pointing triangles show losses and reductions in breeding status. Grey dots indicate no change. The numbers and percentage of tetrads in each category are shown in the left column.
Distribution comparison
On the distribution comparison maps, red dots are used to show presence in the first selected species/atlas and green dots for presence in the second selected species/atlas. Presence in both selections is indicated by grey dots. The numbers of tetrads in each category are shown in the left column. The numbers and percentage of tetrads in each category are shown in the left column.
Habitat comparison
On the habitat comparison maps, green dots are used to show tetrads where the species distribution meets the selected threshold and the selected habitat meets the coverage threshold. Grey dots show where the species was found but the habitat does not exist. Red squares show habitat presence without the bird species. The numbers of tetrads in each category are shown in the left column.
Species maps
Distribution - to view a distribution map, select the atlas and species.
Abundance - to view a relative abundance map, select the atlas and species.
Distribution change - to view a map of the change in distribution between two survey periods, select the two atlases and the species.
Distribution comparison - to view a map comparing the distribution of two species in the same or different survey periods, select the two atlases and the two species.
Habitat comparison - to view a map showing the correlation between the bird distibution and a habitat type, select the atlas and species of interest. For breeding season atlases, the breeding status threshold (presence, possible breeding, probable breeding, confirmed breeding) may be used to control the level of evidence to be compared. Select a habitat dataset and one of the features within that dataset. The habitat threshold sets the minimum percentage coverage of the tetrad needed to count as present.
The habitat datasets Land Cover 1990 (LCM1990), Land Cover 2000 (LCM2000) and Land Cover 2007 (LCM2007) were produced by the Centre for Ecology and Hydrology (CEH). The percentage of habitat in each tetrad is derived from satellite images and digital cartography and gives land cover information for the entire UK. Slightly different habitat classification schemes were used in each survey.