Numbers 1 - 2
This book is so named because the people are numbered twice, with a census 2 years after leaving Egypt, and then a second one just before entering the Promised Land. This was a counting of the men who were 20 years and older, who were eligible to fight in the army, which totaled 603,550, not including the Levites (who served God and His Tabernacle).
Chapter 2 lists the camping order of the tribes, with the Levites and the Tabernacle of meeting located at the center, and three tribes lined up to the east (186,400), three tribes to the south (151,450), three tribes to the west (108,100), and three tribes to the north (157,600).
If you were to fly over this camp from the rising sun (the east), you would see this multitude encamped, somewhat like the shape of the cross lying on the ground, with the Presence of God at the central junction point.