Differential number counts of z ∼ 4 quasar candidates. Blue crosses represent the number counts derived in the entire S16A-Wide2 region. Open squares are the number counts after dividing the region into the four sub-regions (pink: WideA, cyan: WideB, orange: WideC, and gray: WideD). The uncertainties associated with the number count in each sub-region are determined with the Poisson statistics. The open squares in each sub-region are shifted in horizontal direction for clarity. The filled circles show the number counts after correcting for the expected contamination by Galactic stars (green solid line for each sub-region) and the compact galaxies (red open circles). (Color online)