如何在阿尔贝拉等面积投影中使用经纬度对在 cartopy 中进行 plot？

Question

I am trying to plot PM data in lat lon pairs data using cartopy. I tried it using two different projections. (PM25['lat'] has lat values, PM25['lon'] has lon values and val is the grid with PM25 concentrations):

1. Plate Carre and 2. Albera Equal Area Conic projection. I am attaching the code and figures here. My questions are

a) Why do the colors in Albera Equal Area conic projection look smoother?

b) How do I add state borders in conic area projection?

Code for Albera Projection

extent = [-125,-65,25,50]
fig = plt.figure(figsize=(8,4))
ax.set_extent(extent)
ax.coastlines(resolution="110m",linewidth=1)
ax.gridlines(linestyle='--',color='black')
ax.add_feature(cfeature.BORDERS.with_scale('50m'), alpha=1)
ax.add_feature(cfeature.STATES)
projection = ccrs.AlbersEqualArea(central_longitude=-100)
ax.add_feature(COUNTIES, facecolor='none', edgecolor='gray', alpha =0.5)
projection = ccrs.AlbersEqualArea(central_longitude=-100)
fig.add_axes([-.05, -.05, 1.2, 1.2], projection=projection)
ax.add_feature(cfeature.STATES)[enter image description here][1]
clevs = np.arange(0,40)
plt.contourf(PM25['lon'], PM25['lat'], val,clevs, transform=ccrs.PlateCarree(),cmap='viridis',vmin=0, 
vmax =16)

Albera Equal Area Conic Projection

Code for Plate Carre Projection

from matplotlib import colorbar, colors
extent = [-125,-65,25,50]
fig = plt.figure(figsize=(8,4))
ax = plt.axes(projection=ccrs.PlateCarree())
ax.set_extent(extent)
ax.coastlines(resolution="110m",linewidth=1)
ax.gridlines(linestyle='--',color='black')
ax.add_feature(cfeature.BORDERS.with_scale('50m'), alpha=1)
ax.add_feature(cfeature.STATES)
#ax.add_feature(COUNTIES, facecolor='none', edgecolor='gray', alpha =0.5)
clevs = np.arange(0,40)
plt.contourf(PM25['lon'], PM25['lat'], val,clevs, transform=ccrs.PlateCarree(),cmap='viridis',vmin=0, 
 vmax =16)

Plate Carre Projection

Answer 1

a) I think Albers looks smoother maybe just because the projection is different, the figure of projection Plate Carre is squashed into a band.

b) You should set the axes projection firstly just like in Plate Carre plot, then shapefile polygons will show in the figure.

fig = plt.figure(figsize=(8,4))
projection = ccrs.AlbersEqualArea(central_longitude=-100)
ax = plt.axes(projection=projection)
ax.add_feature(...)
ax.add_feature(...)
....