If we use real estate as an indicator of economic health, certain areas in Maine are indeed springing to life.Speakers at the recent MEREDA conference in Portland emphasized again and again that Portland and some other areas of Maine have shortages of housing, office and warehouse space. Bangor, Augusta, Saco-Biddeford and other cities are also encouraged by a growing demand for real estate, one sign of a healthy economy. Developers and contractors are responding to the need, but for now the shortage of space means an increase in rents and compression into surrounding markets.