European Conference on Geographical Information Systems Brussels, Scholten, H. J., Harts, J., & Ottens, H. F. L. (1991). EGIS '91: Proceedings : second European Conference on Geographical Information Systems, Brussels, Belgium April 2-5, 1991. EGIS Foundation.
Παραπομπή σε μορφή Chicago (17η εκδ.)European Conference on Geographical Information Systems Brussels, H. J. Scholten, JanJaap Harts, και Henk F. L. Ottens. EGIS '91: Proceedings : Second European Conference on Geographical Information Systems, Brussels, Belgium April 2-5, 1991. Utrecht, Netherlands: EGIS Foundation, 1991.
Παραπομπή σε μορφή MLA (8th εκδ.)European Conference on Geographical Information Systems Brussels, et al. EGIS '91: Proceedings : Second European Conference on Geographical Information Systems, Brussels, Belgium April 2-5, 1991. EGIS Foundation, 1991.