Network representation of tissue relatedness. Nodes represent collapsed annotation terms and edges represent the correlation between expression in each pair of terms. Only tissues that share a statistically significant number of genes are linked and the strength of the links is proportional to the number of genes the two tissues have in common. Tissues that share very few or no genes repel each other. The system is allowed to reach a low energy level in two-dimensional space under a physical spring model (force directed layout). Collapsed annotation terms are color-coded according to their organ system assignments as used throughout.