The interaction of fluid flow with a circular cylinder is important in many design situations. In the study of fluid-body interaction problems, it is essential that one is familiar with the affected flow structure in terms of its kinematics and related properties. Existing experimental data show that the vertical gap, G, between a horizontal cylinder and a plane boundary is the major parameter that affects the flow structure around the cylinder. In this study, the PIV technique is used to measure the velocity field in a steady, two-dimensional, turbulent flow around a horizontal circular cylinder near a plane boundary. The resulting velocity profiles, streamlines and isovorticity contours are presented for the gap ratios, G/D = 0.0, 0.1, 0.2, 0.3, 0.6, 1.0 and 2.0. Experiments for the seven different G/D ratios are repeated for Reynolds numbers Re-D = 840, 4150 and 9500. Using the measured velocity fields, the effect of gap ratio on the wall boundary-layer separation, the positions of the stagnation and separation points on the cylinder, and the Strouhal number are investigated. Present experimental results indicate that the changes in the flow structure become very slow when G/D >= 0.3, and the wall proximity effect on the flow around the cylinder becomes insignificant when G/D >= 1.0. (C) 2008 Elsevier Ltd. All rights reserved.