One way to picture astride: someone is in the middle of a long step, one leg in front and one behind, and they stop there with the legs still apart. Lower the body a little and whatever is underneath is now between the two legs. That is the whole word — one leg on each side.
astride 可以想成一個人正跨著一大步，一腳在前一腳在後，然後停住，腿還張著。把身體放低一點，中間那樣東西就被兩腿夾住了。這就是整個字要說的事：一邊一隻腳，東西在中間。這個畫面後來被放大到地圖上——身體換成城鎮，中間那樣東西換成一條河。姿勢沒有變，只是尺寸變了。
From the word’s history
Formed from a- plus stride, the long step you take when walking.
astride 由 a- 加上 stride（跨步）組成。stride 是走路時跨出去的那一大步，astride 則是停在那個跨開的狀態上。
Wiktionary, "astride"
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