Add a line on bars with +.

Goal

Run every block and confirm the chart is visible.

df = pd.DataFrame({
    "city": ["Nairobi", "Mombasa", "Kisumu", "Nakuru", "Eldoret"],
    "units": [21, 15, 15, 18, 12],
    "shillings": [2100, 1500, 1480, 1750, 1190],
})
bars = alt.Chart(df).mark_bar().encode(x="city:N", y="units:Q")
pts = alt.Chart(df).mark_circle(size=80, color="orange").encode(x="city:N", y="units:Q")
(bars + pts).properties(width=360, height=220).show()
print("layer")

df = pd.DataFrame({
    "month": ["Jan", "Feb", "Mar", "Apr"] * 2,
    "mm": [48, 55, 92, 150, 22, 18, 40, 80],
    "city": ["Nairobi"] * 4 + ["Mombasa"] * 4,
})
a = alt.Chart(df).mark_line().encode(x="month:N", y="mm:Q", color="city:N")
b = alt.Chart(df).mark_point().encode(x="month:N", y="mm:Q", color="city:N")
(a + b).show()
print("line+point")

df = pd.DataFrame({
    "city": ["Nairobi", "Mombasa", "Kisumu", "Nakuru", "Eldoret"],
    "units": [21, 15, 15, 18, 12],
    "shillings": [2100, 1500, 1480, 1750, 1190],
})
alt.Chart(df).mark_bar().encode(x="city:N", y="units:Q").show()
print("bar")

print("layer = overlay.")