A karyotype is a photomicrograph of an individual's stained chromosomes arranged in a standard format showing the number, size, and shape of each chromosome type.
Each chromosome is characterized by the length of its arms and the location of its centromere, which appears as an indentation or a lightly stained region. Staining methods may result in banding on the chromosomal arms (chromatids); chromosomes can then be identified according to their banding pattern.
Karyotypes are used in low-resolution physical mapping to correlate chromosomal abnormalities with the characteristics of specific diseases.
A physical map is a map of the locations of identifiable landmarks on DNA (e.g., restriction enzyme cutting sites, genes), regardless of inheritance. Distance is measured in base pairs. For the human genome, the lowest-resolution physical map is the banding patterns on the 24 different chromosomes; the highest-resolution map would be the complete nucleotide sequence of the chromosomes.
In biological research, karyotyping is also done to determine or confirm the species that an organism or tissue sample belongs to.
From the science dictionary at http://biotech.icmb.utexas.edu/