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"""
=========================
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.contour`
# method to extract the contours.
contours = aiamap.contour(50000 * u.ct)
##############################################################################
# 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()
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