cat > render_america_points.py << 'EOF'
import json
import numpy as np
import pandas as pd
import datashader as ds
import datashader.transfer_functions as tf
from datashader.utils import lnglat_to_meters


INP = "waterways_america.geojsons"
OUT = "waterways_america.png"

minlon, minlat, maxlon, maxlat = -170.0, -60.0, -25.0, 83.0
x0, y0 = lnglat_to_meters(minlon, minlat)
x1, y1 = lnglat_to_meters(maxlon, maxlat)

W, H = 7000, 7000
cvs = ds.Canvas(plot_width=W, plot_height=H, x_range=(x0, x1), y_range=(y0, y1))

CHUNK_PTS = 3_000_000
xs = np.empty(CHUNK_PTS, dtype="float64")
ys = np.empty(CHUNK_PTS, dtype="float64")
n = 0

agg = None
STRIDE = 1

def flush():
global n, agg
if n == 0:
return
df = pd.DataFrame({"x": xs[:n], "y": ys[:n]})
a = cvs.points(df, "x", "y", agg=ds.count())
agg = a if agg is None else (agg + a)
n = 0

def add_coords(coords):
global n
if not coords:
return
for i in range(0, len(coords), STRIDE):
pt = coords[i]
if not pt or len(pt) < 2:
continue
X, Y = lnglat_to_meters(pt[0], pt[1])
xs[n] = X
ys[n] = Y
n += 1
if n >= CHUNK_PTS:
flush()

with open(INP, "r", encoding="utf-8", errors="ignore") as f:
for line in f:
line = line.strip()
if not line:
continue
try:
feat = json.loads(line)
except json.JSONDecodeError:
continue
geom = feat.get("geometry")
if not geom:
continue
t = geom.get("type")
if t == "LineString":
add_coords(geom.get("coordinates"))
elif t == "MultiLineString":
for coords in geom.get("coordinates") or []:
add_coords(coords)

flush()

img = tf.shade(agg, how="eq_hist")
img.to_pil().save(OUT)
print("OK ->", OUT)
EOF