On Bemidbar 13:25, Oznayim Latorah says that Israel measures 400 parsahs by 400 parsahs. Does this mean that it’s a square? It doesn’t look that way on a map.
This idea is not from the Oznayim L’torah, rather it is mentioned in the gemorah and midrashim in numerous places. The Maharal (Chidushei Agados Rosh Hashana 23a, pg. 125-6) addresses your question, and he even adds to it. He asks that the gemora in Baba Metzia 28a seems to say that Eretz Yisroel was only wide 15 days worth of walking, and 400 parsa is 40 days? He answers that what is meant by 400 parsa by 4—parsa is only a figurative term, because 4 represents physical completeness, and so does 100, therefore 400x 400 is meant to say that Eretz Yisroel is complete in all ways. Physically though it was smaller than that.