1)
What are "Totze'os ha'Ir"?
1.
Rashi: They are its gates, in its four directions. Radak ? there are three gates in each direction, one for each Shevet.
2)
What is "Midah"?
1.
Rashi: It is the measure, Kaneh ? the gates are 4500 Kanim in the north. Malbim ? this is 13.5 Mil, for a Kaneh is six Amos.