“in the direction of the north.” In the vision, Ezekiel was placed at the entrance to the gate from the inner court of the Temple that looks north, i.e., the north gate of the inner court (Ezek. 8:3). He was told to look north and when he did he saw the image of jealousy in the entrance to the gate. So we know from this information that in the vision Ezekiel was set down inside the inner court, not outside it. If Ezekiel was outside the gate he would have had to have looked southward to see an idol in the north gate.
“the Altar Gate.” The Hebrew is “the gate of the altar,” but that is unclear in English because the altar did not have a gate, the gate was roughly adjacent to the altar in the inner courtyard, so it was called “the Altar Gate.”
“image of jealousy.” This is a genitive of production, an image (an idol) that produced jealousy, that is, the idol made God jealous.