Pennsylvania Society for Ornithology

Pennsylvania Breeding Bird Atlas

Sample Block Layout

The map below shows how to divide the Delorme Atlas pages into Breeding Bird Atlas Blocks.

The sample is pages 48 and 49. The two combined pages are divided into 4 rows and 7 columns. This creates 28 7.5minute quadrangles.

The rows are labeled top to bottom A, B, C, and D. The columns are numbered left to right 1 through 7.

Each quadrangle in turn is divided into 3 rows and 2 columns. Each of these divisions constitutes one block. The blocks are numbered 1 through 6 starting at the top left and ending at the bottom right (see sample).

In the sample below, quadrangle C3 is divided into its blocks.

Each block is designated by the Page Number, Quadrangle Number, and Block Number. In the sample below, the lower right block in C3 would be designated as 48C36 (Page 48, Quadrangle C3, Block 6).