我有一个华盛顿的图表，DC公寓价格，我想其中一个下拉选项是“年建成”.这是我到目前为止的代码：

dropdown = alt.binding_select (options=["Square Feet", "Year built", "Rooms"], name="Select a size variable:")

# Create a new selection that uses my dynamic query widget
selection = alt.selection(type="single", fields=['column'], bind=dropdown, init={'column':'Square Feet'})

alt.Chart(altdat, title='Washington, D.C. condos, by price').transform_fold(
    ["Square Feet", "Year built", "Rooms"],
    as_=['column', 'value']
).transform_filter(
    selection
).mark_circle().encode(
    x = alt.X('Longitude', scale=alt.Scale(domain=[altdat['Longitude'].min(), altdat['Longitude'].max()])),
    y = alt.Y("Latitude", scale=alt.Scale(domain=[altdat['Latitude'].min(), altdat['Latitude'].max()])),
    color=alt.Color('Price (city appraisal)', scale=alt.Scale(scheme='redyellowgreen', reverse=True)),
    size="value:Q",
    tooltip=["WARD", "Square Feet", "Year built", "Rooms"]
).add_selection(selection
).properties(
    width=600,
    height=600
).interactive()

但是，当我选择年份作为下拉列表时，刻度从0到2000，使其无效。Altair image如何仅将年份变量的刻度从1800调整到2000？我仍然希望平方英尺从0到2000。谢谢！