Walter Isard, professor emeritus of city and regional planning and economics who had founding roles in the fields of regional science and peace science, died Nov. 6 in Drexel Hill, Pa. He was 91.

A member of the American Academy of Arts and Sciences and the National Academy of Sciences, Isard was an influential scholar of regional science methodology and theory, regional economics and development, and peace economics and science. His research ranged from interregional constructs and systems of cities and regions to the economic and social consequences of atomic power and industrial complexes, and theories of individual behavior and decision-making.

Isard also pursued interests in conflict management and resolution, disarmament and peace science. He founded what is now the Peace Science Society in the early 1960s to apply analytical tools to the study of international conflicts. He also founded the Journal of Peace Science, later renamed Conflict Management and Peace Science.

He was the author of more than 300 published articles and 21 books, including "Location and Space Economy" (1956); "Methods of Interregional and Regional Analysis" (1960, updated 1998) and "General Theory" (1969).

Isard established an interdisciplinary movement in regional and urban research in North America, Europe and Asia, beginning in 1948 when he initiated meetings of leading economists, geographers, sociologists and demographers, and encouraged them to cross disciplinary boundaries and apply analytical methods to emerging urban, regional and environmental policy issues.

He organized a conference program in 1954 at the Allied Social Science Associations meetings in Detroit, where 60 scholars endorsed the formation of a Regional Science Association. The association now has about 4,500 members worldwide; it established its Founder's Medal in his honor in 1978. He came to Cornell the following year as a professor of economics and continued his active research after his retirement from teaching in 1989.

In April 2009, the graduate field of regional science hosted an event in Sibley Hall celebrating Isard's 90th birthday and 35 years of regional science at Cornell.

Born in 1919 in Philadelphia, Isard graduated with distinction from Temple University in 1939 with a degree in mathematics. He earned his Ph.D. from the University of Chicago in 1942.

A conscientious objector during WWII, he served in the Civilian Public Service. During night shifts at a state mental hospital, he translated into English the works of German location theorists. His teaching appointments after the war included Harvard's first economics course on location theory and regional development.

Isard taught regional economics at M.I.T. before joining the University of Pennsylvania economics faculty as a professor in 1956. He founded Penn's Regional Science Department and the Journal of Regional Science in 1958.

He is survived by his wife, Caroline, and several children and grandchildren. A private funeral will be held for the family, and a memorial service is being planned at Cornell.