Specificity threshold accurately predicts spatial expression restriction. A plot of specificity (S) versus cumulative tag types represented shows the distribution of tags into tags with high (S > 0.1; top), medium (0.001 > S < 0.1, middle), and low (S < 0.001, bottom) S values. Representative in situ hybridization staining patterns from TS22 whole embryo saggital sections obtained from GenePaint are shown for each specificity group. Relevant GenePaint probe IDs can be found in Additional data file 4. Arrows indicate the location of the pancreas (p).