At the beginning of Numbers, God has Moses take a census of all the people for each of the tribes in Israel. Each male adult, over the age of 20, is counted in order for the land to be given out on a proportional basis between the tribes. An interesting thing happens when the tribes are given the land.
Num 2:9 All those listed of the camp of Judah, by their companies, were 186,400. They shall set out first on the march.
Num 2:16 All those listed of the camp of Reuben, by their companies, were 151,450. They shall set out second.
Num 2:24 All those listed of the camp of Ephraim, by their companies, were 108,100. They shall set out third on the march
Num 2:31 All those listed of the camp of Dan were 157,600. They shall set out last, standard by standard.”
There are more tribes then what is listed, but the other tribes were grouped into the “main” tribe. Judah and those tribes associated with the group were to camp to the east of the Tabernacle. Ruben and those tribes are on the south side, Ephraim and those tribes were on the west side and Dan and those tribes were on the north side.
If you lay them out, here is kind of what it looked like: