Why Offer at the Door?
The chapter begins with the voluntary offerings brought from the "herd" and references the sacrifice of a bullock.
If his offering be a burnt sacrifice of the herd, let him offer a male
without blemish: he shall offer it of his own voluntary will at the
door of the tabernacle of the congregation before the LORD. (Leviticus
And he shall put his hand upon the head of the burnt offering; and it
shall be accepted for him to make atonement for him. (Leviticus 1:4,
And he shall kill the bullock before the LORD: and the priests,
Aaron's sons, shall bring the blood, and sprinkle the blood round
about upon the altar that is by the door of the tabernacle of the
congregation. (Leviticus 1:5, KJV)
A bovine sacrifice, as this would be, is a large animal. The word "bullock" might better be stated as "bull" in modern English--it was a male, as it says in verse 3. A bull is not typically as docile as a sheep would be. It is quite possible that God had the safety of those inside the sanctuary in mind when giving instructions for the bulls to be sacrificed "at the door."
Where Was the Door?
The door of the tabernacle, incidentally, would have been on the east side. The ark of the covenant, in the Most Holy Place, would have been to the west side of the tabernacle. This is determined from the layout of the exterior walls of the tabernacle, detailed below.
And thou shalt make boards for the tabernacle of shittim wood standing
up. (Exodus 26:15, KJV)
Ten cubits shall be the length of a board, and a cubit and a half
shall be the breadth of one board. (Exodus 26:16, KJV)
Two tenons shall there be in one board, set in order one against
another: thus shalt thou make for all the boards of the tabernacle.
(Exodus 26:17, KJV)
And thou shalt make the boards for the tabernacle, twenty boards on
the south side southward. (Exodus 26:18, KJV)
And thou shalt make forty sockets of silver under the twenty boards;
two sockets under one board for his two tenons, and two sockets under
another board for his two tenons. (Exodus 26:19, KJV)
And for the second side of the tabernacle on the north side there
shall be twenty boards: (Exodus 26:20, KJV)
And their forty sockets of silver; two sockets under one board, and
two sockets under another board. (Exodus 26:21, KJV)
And for the sides of the tabernacle westward thou shalt make six
boards. (Exodus 26:22, KJV)
And two boards shalt thou make for the corners of the tabernacle in
the two sides. (Exodus 26:23, KJV)
And they shall be coupled together beneath, and they shall be coupled
together above the head of it unto one ring: thus shall it be for them
both; they shall be for the two corners. (Exodus 26:24, KJV)
And they shall be eight boards, and their sockets of silver, sixteen
sockets; two sockets under one board, and two sockets under another
board. (Exodus 26:25, KJV)
With the north and south sides having 20 boards each, and the west side having 6 boards--8 including the corners, the structure is clearly located in an east-west direction. No boards are specified for the east side, which leaves it to be the opening that was covered by "a hanging" (a curtain), detailed later in the chapter.
By putting the ark on the west end of the sanctuary and of the entire tabernacle enclosure, it leaves the entrance to be on the east. This was important because the surrounding nations were involved in sun worship, and would worship the sun at its rising in the morning. Looking westward through the gate on the east, one would be faced in the opposite direction from the sun in the morning.
Why Put the Animal of the Flock on the North?
The placement of the animal from the flock on the north side of the altar at the time of sacrifice would also prevent people from seeing the sun behind it, whether it was a morning sacrifice (where the sun would be in the east) or an evening sacrifice (sun in the west). As another answer already suggests, God also associates the north with the direction of His city of "Mount Zion" (Psalm 48:2). The people were to look to Him, and not to the sun, for salvation.
In a later description of apostasy, it is clear that the elders would go exactly contrary to God's arrangement.
And he brought me into the inner court of the LORD's house, and,
behold, at the door of the temple of the LORD, between the porch and
the altar, were about five and twenty men, with their backs toward the
temple of the LORD, and their faces toward the east; and they
worshipped the sun toward the east. (Ezekiel 8:16, KJV)
This is the evil that God intends to avoid by placing the sacrifices where the sun will not be in view at the moment of their offering.
Offerings from the flock would occur both in the morning and in the evening as part of the continual worship of God.
Behold, I build an house to the name of the LORD my God, to dedicate
it to him, and to burn before him sweet incense, and for the continual
shewbread, and for the burnt offerings morning and evening, on the
sabbaths, and on the new moons, and on the solemn feasts of the LORD
our God. This is an ordinance for ever to Israel. (2 Chronicles 2:4,
To avoid any possible connection with sun worship, the offering was to be so located as to prevent the onlookers from seeing the sun behind their sacrifice, lest they be tempted to consider it the object of their worship.