In a nation, a centre of power where innovation, technology, and employment are at a high level, such as Madrid or south-east England. See Harrison (2007) J. Econ. Geog. 7, 3 on England’s Core Cities Group, and Pain, no date, GaWC Res. Bull. 220 on the London core and the global ‘mega-city region’.

http://www.etsg.org/ETSG2006/papers/Brand.pdf Brand and Bhatti (2006) on the core region of Madrid.