The shape and distribution of boundaries within and between grains have an influential effect onthe microstructure evolution of polycrystalline polar ice. Indeed, microstructural processes likepolygonization, grain growth and recrystallization are directly affected by the (sub-)grainboundary arrangement and hierarchy. To map the (sub-)grain boundaries in a thick section of icewe used a CCD video camera system and a computer controlled xy-stage attached to an opticalmicroscope. Samples from three different depths were detailled mapped in the field. Theboundaries were classified according to their shape, intensity and (in the case of sub-boundaries) inclination relative to the surrounding slip lines. An extensive pinning and/or bulgingof grain boundaries by inclusions and subgrain boundaries were identified, indicating thatboundary migration seems to depend strongly on the deformation and inclusion content, even atshallow depths. A surprisingly high amount of bent and polygonized slip lines were also found atshallow depths, evidencing that the intracrystalline deformation is highly inhomogeneous evenclose to the ice sheet surface. The origins of frequent subgrain loops are also discussed.