Surface models and the spatial structure of population variables: Exploring smoothing effects using Northern Ireland grid square data

•Use of ancillary data produces more accurate gridded population estimates from area data than does a smoothing approach.•Using ancillary data and smoothing in combination produces the most accurate gridded estimates.•Smoothing has a bigger impact on gridded estimates for smaller source zones than for larger source zones.•Smoothing is likely to provide greater gains when a variable is more spatially continuous.