Line Chart with Varying Size

This is example of using the trail marker to vary the size of a line.

Method syntax

import altair as alt
from vega_datasets import data

source = data.wheat()

alt.Chart(source).mark_trail().encode(
    x='year:T',
    y='wheat:Q',
    size='wheat:Q'
)

Attribute syntax

import altair as alt
from vega_datasets import data

source = data.wheat()

alt.Chart(source).mark_trail().encode(
    x='year:T',
    y='wheat:Q',
    size='wheat:Q'
)
# No channel encoding options are specified in this chart
# so the code is the same as for the method-based syntax.