How is the "line" in the title of Qiantang Spring Tour reflected in the poem?

Spring outing in Qiantang Lake

Bai Juyi

From the north side of Gushan Temple to the west side of Jiating, the lake is just level with the embankment, with low clouds and waves on the lake.

Several early orioles raced to the sunny tree, and their new swallows were carrying mud in their nests.

Colorful spring flowers will gradually fascinate people's eyes, and shallow spring grass can barely cover the horseshoe.

I love the beauty on the east bank of the West Lake, and I can't get enough of it, especially the white sand embankment under the green poplar.

According to the itinerary, the poet listed some place names in his poems, from "Gushan Temple" to "Hudong" and "Baishadi". At the same time, things have also changed, from "early warbler" to "new swallow", from "disorderly flower" to "shallow grass" It is these images that vividly embody the "line".