"""
=========================
Finding contours of a map
=========================

This example shows how to find and plot contours on a map.
"""
import matplotlib.pyplot as plt

import astropy.units as u

import sunpy.map
from sunpy.data.sample import AIA_193_IMAGE

###############################################################################
# Start by loading the sample data.

aiamap = sunpy.map.Map(AIA_193_IMAGE)

###############################################################################
# In finding a set of contours, we have to provide the level to contour in the
# same units as the map data. To find out the units we can inspect
# `sunpy.map.GenericMap.unit`.

print(aiamap.unit)

###############################################################################
# We can see that the units of this map are ``ct``, or counts. We can now
# chose a contour level, and use the :meth:`~sunpy.map.GenericMap.find_contours`
# method to extract the contours.

contours = aiamap.find_contours(50000 * u.DN)

##############################################################################
# Finally, we can plot the map, and add each of the contours in turn.

fig = plt.figure()
ax = fig.add_subplot(projection=aiamap)
aiamap.plot(axes=ax)
for contour in contours:
    ax.plot_coord(contour)
plt.show()
