Effect of spatial resolution on field-averaged parameters. The grayscale image shows the distributions of (T, β) values calculated from IRIS and Planck data for pixels. The contours show the distribution separately for pixels below (blue contours) and above (red contours) the average column density in each field. The contours are drawn at levels of 20%, 50%, and 90% of the maximum value (data points per area) for distributions calculated from surface brightness data at 5′ (solid contours) or 10′ (dashed contours) resolution. The dotted contours (50% level only) correspond to a case where the surface brightness values of all pixels below or above the median value (per field) are averaged before (T, β) calculation.