Croatia proper (; ) is one of the four historical regions of the Republic of Croatia, together with Dalmatia, Slavonia, and Istria. It is located between Slavonia in the east, the Adriatic Sea in the west, and Dalmatia to the south. The region is not officially defined, and its borders and extent are described differently by various sources. Croatia proper is the most significant economic area of the country, contributing well over 50% of Croatia's gross domestic product. The capital of both Croatia proper, and the Republic of Croatia, Zagreb, is the largest city and most important economic centre in the region.