why the scatter plot can not be on the map created by cartopy

plt.figure(figsize = (10,10),dpi =150)
ax = plt.axes(projection=ccrs.EuroPP())

ax.coastlines(resolution='50m')
ax.set_extent([-16., 5., 49., 61.])


plt.scatter([10.,15.],[52.5,55.],marker='o',s = 100,
            transform = ccrs.EuroPP(), color = "red")

ax.gridlines(draw_labels=True)
plt.show()

Why there is only a map, and the scatter plot cannot be on the map?

Solution

The transform you specify for the scatter should be the projection of the data, not the map. It looks as if they are lat/lon values (epsg:4326)? (Technically they could of course be EuroPP coordinates, just really close to the origin)

Where do you expect those points to be more or less?

map_proj = ccrs.EuroPP()
data_proj = ccrs.PlateCarree()

fig, ax = plt.subplots(
    figsize=(10,10), dpi=76, 
    subplot_kw=dict(projection=map_proj),
)

ax.scatter(
    [10.,15.],[52.5,55.], marker='o', s=100, 
    color="r", transform=data_proj,
)

ax.coastlines(resolution='50m')
ax.set_extent([-5., 20., 49., 61.], crs=data_proj)
ax.gridlines(draw_labels=True)