Optimal estimation is applied to contouring and analysis of hydrographic sections. Measured fields, such as temperature and salinity, and derived fields, such as geostrophic velocity, are decomposed into large-scale and small-scale components. First, a heavily sampled basin-scale field is estimated and subtracted from the data. A small-scale field, barely resolved by the hydrography, is then found from the residuals. The power and utility of the technique are illustrated by means of examples, using a short section from the Straits of Florida and a transatlantic section along 24°N. Abstract Optimal estimation is applied to contouring and analysis of hydrographic sections. Measured fields, such as temperature and salinity, and derived fields, such as geostrophic velocity, are decomposed into large-scale and small-scale components. First, a heavily sampled basin-scale field is estimated and subtracted from the data. A small-scale field, barely resolved by the hydrography, is then found from the residuals. The power and utility of the technique are illustrated by means of examples, using a short section from the Straits of Florida and a transatlantic section along 24°N.