The letter indicates Ezekiel's location as he is guided through the mountain site area of all the buildings in the sanctuary of the LORD's house on Mt. Zion. The texts (cited from the prophecy) show the particular scene at his position as he gazes at each structure within the sanctuary. Follow along and -- carefully! -- observe with Ezekiel.
These locations are found on Diagram A, following this list of the scenes which Ezekiel sees...
a -- Set upon the mountain before the city wall, before a gate, 40:1-5.
b -- Up the steps and through the gate, 40:6.
c -- Into the court outside the gate's "house," 40:17.
d -- A gate of the Inner Court, 40:23.
e -- Brought toward the south gate, 40:24.
f -- A gate of the Inner Court, 40:27.
g -- Brought into the Inner Court via its south gate, 40:28.
h -- Brought into the Inner Court to its east gate, 40:32.
i -- Brought to the north gate, 40:35.
j -- The entrance to the chambers by the gate house, 40:38.
k -- Outside the Inner Gate, in the Inner Court, 40:44.
l -- Measuring the court and its altar, 40:47.
m -- Measuring the porch of the temple, 40:48.
n -- Measuring the temple itself, 41:1.
o -- Observing the elevation surrounding the "house," 41:8.
p -- Observing the building toward the west, 41:12.
q -- Brought in the northern direction into a court outside (between the temple and the building), 42:1
r -- Into chambers opposite the separate place, 42:2, 13.
s -- Brought forth toward the east gate, 42:15.
t -- Measuring the exterior sides of the "house," 42:16-20.
u -- Brought to the east gate, 43:1.
v -- Brought into the Inner Court, 43:5.
w -- Brought back in the direction of the east gate, 44:1.
x -- Brought via the way of the north gate, in the presence of the temple, 44:4.
y -- Brought through an entrance at the side of the gate, 46:19.
z -- Brought into the Outer Court, 46:21.
aa -- Brought again to the temple's door, 47:1.
bb -- Brought out onto the "common" by the way of the north gate and led around its way to the vicinity of the outer east gate, 47:2.
cc -- Measuring the water's depth, 47:3.
dd -- Returned to the river bank, 47:6-7.