Wikipedia
Ziemia (, Land) is a historical unit of administration in Poland. In the Polish language, the term is not capitalized (ziemia chełmińska, Chelmno Land; not Ziemia Chełmińska). All ziemias are named after main urban centers (or gords) of a given area: ziemia krakowska (after Krakow), or ziemia lubelska (after Lublin). In some cases, the suffix "-szczyzna" is added to the name of a ziemia: ziemia lubelska is also called Lubelszczyzna, while ziemia opolska (named after Opole) - Opolszczyzna.
The term ziemia appeared for the first time in medieval Poland (12th-13th centuries), after the fragmentation of Poland. It referred to a former princedom or duchy, which was unified with the Polish Kingdom, and lost its political sovereignty, but retained its hierarchy of officials and bureaucracy. From around the 14th century some of the former princedoms, now ziemias, were assigned to officials known as voivodes and became primary units of administration known as voivodeships (provinces). Therefore, the Duchy of Sandomierz was turned into the Land of Sandomierz, which in the early 14th century became Sandomierz Voivodeship.
However in some cases ziemias were not transformed into voivodeships. They were subordinated to a voivodeship and a certain voivode, but nevertheless retained some distinct privileges and properties, such as often having their own sejmik (regional parliament), and were still referred to as a ziemia, not a voivodeship. Some voivodeships, such as Ruthenian Voivodeship or Masovian Voivodeship, consisted of several ziemias, each divided into counties. Over subsequent centuries, ziemias became increasingly integrated into their voivodeships and lost most of their autonomy.
Today they are not units of administration, and in modern Poland are only generic geographical terms referring to certain parts of Poland. Currently, the term ziemia may apply to any area, historic or not, which is located around a main town or city.