trail marker is like the
line marker, but it allows properties of
the line (such as thickness) to vary along the length of the line.
This shows a simple example of the trail mark using stock prices.
import altair as alt from vega_datasets import data stocks = data.stocks.url alt.Chart(stocks).mark_trail().encode( x='date:T', y='price:Q', size='price:Q', color='symbol:N' )