class_docstr: Base class for formatting ticks on geographical axes using a
  rectangular projection (e.g. Plate Carree, Mercator).
class_docstr_tok: ["Base","class","for","formatting","ticks","on","geographical","axes","using","a","rectangular","projection","(","e.g",".","Plate","Carree",",","Mercator",")","."]
docstr: Given a single value, a target projection and a source CRS,
  transform the value from the source CRS to the target
  projection, returning a single value.
code: def _apply_transform(self, value, target_proj, source_crs):
      """
      Given a single value, a target projection and a source CRS,
      transform the value from the source CRS to the target
      projection, returning a single value.
  
      """
      raise NotImplementedError(
          "A subclass must implement this method."
      )
  
imports: import matplotlib
  from matplotlib.ticker import Formatter, MaxNLocator
  import numpy
  import cartopy.crs
  from cartopy.mpl.geoaxes import GeoAxes
label_desc: Use image node_id 10 for calling the _PlateCarreeFormatter obj's underlying member method code with example usage: obj._apply_transform(value, target_proj, source_crs) without return types