diff --git a/docs/sphinx/source/reference/scaling.rst b/docs/sphinx/source/reference/scaling.rst
index 75599282e2..34f1ad3a5c 100644
--- a/docs/sphinx/source/reference/scaling.rst
+++ b/docs/sphinx/source/reference/scaling.rst
@@ -9,3 +9,4 @@ Methods for manipulating irradiance for temporal or spatial considerations
    :toctree: generated/
 
    scaling.wvm
+   scaling.latlon_to_xy
diff --git a/docs/sphinx/source/whatsnew/v0.9.6.rst b/docs/sphinx/source/whatsnew/v0.9.6.rst
index 50b11750bf..e5cb007a06 100644
--- a/docs/sphinx/source/whatsnew/v0.9.6.rst
+++ b/docs/sphinx/source/whatsnew/v0.9.6.rst
@@ -17,6 +17,9 @@ Breaking Changes
   (:pull:`1768`)
 * For consistency with the rest of pvlib, the ``tilt`` parameter is renamed
   to ``surface_tilt`` in :py:func:`pvlib.soiling.hsu`. (:issue:`1717`, :pull:`1738`)
+* Several undocumented functions in :py:mod:`pvlib.iotools.midc`,
+  :py:mod:`pvlib.iotools.srml`, and :py:mod:`pvlib.iotools.surfrad`
+  are now private. (:issue:`1756`, :pull:`1769`)
 * The following, originally deprecated in :ref:`whatsnew_0900`, is now removed:  (:pull:`1770`)
 
   - The :py:class:`pvlib.tracking.SingleAxisTracker` class
diff --git a/pvlib/iotools/midc.py b/pvlib/iotools/midc.py
index 063326b60c..75cc5609a7 100644
--- a/pvlib/iotools/midc.py
+++ b/pvlib/iotools/midc.py
@@ -102,7 +102,7 @@
 }
 
 
-def format_index(data):
+def _format_index(data):
     """Create DatetimeIndex for the Dataframe localized to the timezone provided
     as the label of the second (time) column.
 
@@ -126,7 +126,7 @@ def format_index(data):
     return data
 
 
-def format_index_raw(data):
+def _format_index_raw(data):
     """Create DatetimeIndex for the Dataframe localized to the timezone provided
     as the label of the third column.
 
@@ -200,9 +200,9 @@ def read_midc(filename, variable_map={}, raw_data=False, **kwargs):
     """
     data = pd.read_csv(filename, **kwargs)
     if raw_data:
-        data = format_index_raw(data)
+        data = _format_index_raw(data)
     else:
-        data = format_index(data)
+        data = _format_index(data)
     data = data.rename(columns=variable_map)
     return data
 
diff --git a/pvlib/iotools/srml.py b/pvlib/iotools/srml.py
index 6e7675482c..86b3e3aeb6 100644
--- a/pvlib/iotools/srml.py
+++ b/pvlib/iotools/srml.py
@@ -61,12 +61,12 @@ def read_srml(filename, map_variables=True):
        `http://solardat.uoregon.edu/ <http://solardat.uoregon.edu/>`_
     """
     tsv_data = pd.read_csv(filename, delimiter='\t')
-    data = format_index(tsv_data)
+    data = _format_index(tsv_data)
     # Drop day of year and time columns
     data = data[data.columns[2:]]
 
     if map_variables:
-        data = data.rename(columns=map_columns)
+        data = data.rename(columns=_map_columns)
 
     # Quality flag columns are all labeled 0 in the original data. They
     # appear immediately after their associated variable and are suffixed
@@ -92,7 +92,7 @@ def read_srml(filename, map_variables=True):
     return data
 
 
-def map_columns(col):
+def _map_columns(col):
     """Map data element numbers to pvlib names.
 
     Parameters
@@ -120,7 +120,7 @@ def map_columns(col):
         return col
 
 
-def format_index(df):
+def _format_index(df):
     """Create a datetime index from day of year, and time columns.
 
     Parameters
diff --git a/pvlib/iotools/surfrad.py b/pvlib/iotools/surfrad.py
index 7f4d86e46a..d3e40d86a2 100644
--- a/pvlib/iotools/surfrad.py
+++ b/pvlib/iotools/surfrad.py
@@ -150,7 +150,7 @@ def read_surfrad(filename, map_variables=True):
                        header=None, names=SURFRAD_COLUMNS)
     file_buffer.close()
 
-    data = format_index(data)
+    data = _format_index(data)
     missing = data == -9999.9
     data = data.where(~missing, np.NaN)
 
@@ -159,7 +159,7 @@ def read_surfrad(filename, map_variables=True):
     return data, metadata
 
 
-def format_index(data):
+def _format_index(data):
     """Create UTC localized DatetimeIndex for the dataframe.
 
     Parameters
diff --git a/pvlib/tests/iotools/test_midc.py b/pvlib/tests/iotools/test_midc.py
index 1c5c38b6a2..96992babba 100644
--- a/pvlib/tests/iotools/test_midc.py
+++ b/pvlib/tests/iotools/test_midc.py
@@ -27,9 +27,9 @@ def test_mapping():
 #                          '?site=UAT&begin=20181018&end=20181019')
 
 
-def test_midc_format_index():
+def test_midc__format_index():
     data = pd.read_csv(MIDC_TESTFILE)
-    data = midc.format_index(data)
+    data = midc._format_index(data)
     start = pd.Timestamp("20181014 00:00")
     start = start.tz_localize("MST")
     end = pd.Timestamp("20181014 23:59")
@@ -39,16 +39,16 @@ def test_midc_format_index():
     assert data.index[-1] == end
 
 
-def test_midc_format_index_tz_conversion():
+def test_midc__format_index_tz_conversion():
     data = pd.read_csv(MIDC_TESTFILE)
     data = data.rename(columns={'MST': 'PST'})
-    data = midc.format_index(data)
+    data = midc._format_index(data)
     assert data.index[0].tz == pytz.timezone('Etc/GMT+8')
 
 
-def test_midc_format_index_raw():
+def test_midc__format_index_raw():
     data = pd.read_csv(MIDC_RAW_TESTFILE)
-    data = midc.format_index_raw(data)
+    data = midc._format_index_raw(data)
     start = pd.Timestamp('20181018 00:00')
     start = start.tz_localize('MST')
     end = pd.Timestamp('20181018 23:59')
diff --git a/pvlib/tests/iotools/test_srml.py b/pvlib/tests/iotools/test_srml.py
index 9939374ebf..8bd8c94349 100644
--- a/pvlib/tests/iotools/test_srml.py
+++ b/pvlib/tests/iotools/test_srml.py
@@ -70,8 +70,8 @@ def test_read_srml_dt_index(url, year, month):
     ('2001', '2001'),
     ('2017', 'dni_7')
 ])
-def test_map_columns(column, expected):
-    assert srml.map_columns(column) == expected
+def test__map_columns(column, expected):
+    assert srml._map_columns(column) == expected
 
 
 @pytest.mark.remote_data