A gigapixel macro image is a digital image bitmap composed of one billion (109) pixels (picture elements), or 1000 times the information captured by a 1 megapixel digital camera.
Creating such high-resolution images involves making mosaics (image stitching) of a large number of high-resolution digital photographs which are then combined into a single image.
Gigapixel macro images are made by 'stacking' a number of photographs together in order to increase the depth of field and then stitching the resulting images together in a technique known as 'stack and stitch'.
Such images are usually very large in size and cannot be easily viewed.
Such techniques are familiar in everyday use in e.g. Google Maps.