"By the flank of the altar northward" (Leviticus 1:11) means that the flank shall be on the north. Where then are its front parts? On the south. From this you have learned that the ramp was on the south. Rabbi Judah says: "and its steps shall face east" (Ezekiel 43:17) means that one ascends it and turns to his right, toward the east. From this we have learned that the ramp was on the south.
How the Verse Places the Altar Ramp on the South
Yalkut Shimoni on Torah 446:2
עַל יֶרֶךְ הַמִּזְבֵּחַ צָפֹנָה, שֶׁיְּהֵא יָרֵךְ בַּצָּפוֹן הֵיכָן הֵן פָּנָיו, בַּדָּרוֹם, הָא לָמַדְתָּ שֶׁהַכֶּבֶשׁ בַּדָּרוֹם רַבִּי יְהוּדָה אוֹמֵר (יחזקאל מג, יז) "וּמַעֲלֹתֵהוּ פְּנוֹת קָדִים", שֶׁיְּהֵא עוֹלֶה לוֹ וּפוֹנֶה לִימִינוֹ לְמִזְרָח, הָא לָמַדְנוּ שֶׁהַכֶּבֶשׁ בַּדָּרוֹם.