diff --git a/.gitignore b/.gitignore
index ba74660..a7f1ff1 100644
--- a/.gitignore
+++ b/.gitignore
@@ -55,3 +55,6 @@ docs/_build/
 
 # PyBuilder
 target/
+
+# IDE
+.idea/
\ No newline at end of file
diff --git a/nilearn_sandbox/_utils/__init__.py b/nilearn_sandbox/_utils/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/nilearn_sandbox/_utils/map_alignment.py b/nilearn_sandbox/_utils/map_alignment.py
new file mode 100644
index 0000000..db1fbda
--- /dev/null
+++ b/nilearn_sandbox/_utils/map_alignment.py
@@ -0,0 +1,139 @@
+import nibabel
+import numpy as np
+from numpy.testing import assert_array_almost_equal, \
+    assert_raises
+from sklearn.utils.linear_assignment_ import linear_assignment
+from nilearn.input_data import MultiNiftiMasker
+from nilearn._utils import check_niimg_4d
+
+
+def _spatial_correlation_flat(these_components, those_components):
+    """Compute the spatial covariance betwwen two 2D ndarray
+
+    Parameters
+    ----------
+    these_components: ndarray
+        Shape (n_compoennts, n_features) First component set
+    those_components: ndarray
+        Shape (n_components, n_features) Second component set
+
+    Returns
+    -------
+    corr: ndarray,
+        Shape (n_components, n_components) : correlation matrix
+
+    """
+    this_S = np.sqrt(np.sum(these_components ** 2, axis=1))
+    this_S[this_S == 0] = 1
+    these_components /= this_S[:, np.newaxis]
+
+    that_S = np.sqrt(np.sum(those_components ** 2, axis=1))
+    that_S[that_S == 0] = 1
+    those_components /= that_S[:, np.newaxis]
+    corr = these_components.dot(those_components.T)
+    these_components *= this_S[:, np.newaxis]
+    those_components *= that_S[:, np.newaxis]
+    return corr
+
+
+def _align_many_to_one_flat(reference, target_list, inplace=False):
+    """Align target_list with reference using linear_assignment"""
+    if not isinstance(target_list, list):
+        return _align_one_to_one_flat(reference, target_list, inplace=inplace)
+    if not inplace:
+        res = []
+    for i, target_components in enumerate(target_list):
+        if inplace:
+            _align_one_to_one_flat(reference, target_components,
+                                  inplace=True)
+        else:
+            res.append(_align_one_to_one_flat(reference, target_components,
+                                             inplace=False))
+    if inplace:
+        res = target_list
+    return res
+
+
+def _align_one_to_one_flat(base_components, target_components, inplace=False):
+    """Align target_components with base_components using linear_assignment"""
+    indices = linear_assignment(-_spatial_correlation_flat(base_components,
+                                                         target_components))
+
+    if inplace:
+        target_components[indices[:, 0]] = target_components[indices[:, 1]]
+    else:
+        new_target = np.empty_like(target_components)
+        new_target[indices[:, 0]] = target_components[indices[:, 1]]
+        target_components = new_target
+    return target_components
+
+
+def spatial_correlation(masker, this_img, that_img):
+    """Compute the spatial covariance betwwen two 2D ndarray
+
+    Parameters
+    ----------
+    these_components: nii-like image,
+        4D image with n_components i the 4-th dim : First component set
+    those_components: nii-like image,
+        4D image with n_components i the 4-th dim : Second component set
+
+    Returns
+    -------
+    corr: ndarray,
+        Shape (n_components, n_components) : correlation matrix
+    """
+    this_flat = masker.transform(this_img)
+    that_flat = masker.transform(that_img)
+    return _spatial_correlation_flat(this_flat, that_flat)
+
+
+def align_many_to_one_nii(masker, reference_img, target_imgs):
+    """Align provided Nifti1Image with a reference, unmasking data using
+    provided mask
+
+    Parameters
+    ----------
+        masker: BaseMasker,
+            Masker used to unmask provided Nifti1Image
+
+        reference_img: nii-like image,
+            Component map used as reference for alignment
+
+        target_imgs: list of nii-like images,
+            Components maps to be aligned
+
+    Returns
+    -------
+        new_target_imgs: list of nii-like images,
+            Aligned components maps, in the same order as provided
+    """
+    reference_flat = masker.transform(reference_img)
+    target_flats = masker.transform(target_imgs)
+    _align_many_to_one_flat(reference_flat, target_flats, inplace=True)
+    if isinstance(target_flats, list):
+        return [masker.inverse_transform(target_flat) for target_flat
+                in target_flats]
+    else:
+        return masker.inverse_transform(target_flats)
+
+
+def align_list_with_last_nii(masker, imgs):
+    """Align provided Nifti1Image with last element of the list
+
+    Parameters
+    ----------
+        masker: BaseMasker,
+            Masker used to unmask provided Nifti1Image
+
+        imgs: list of nii-like images,
+            Components maps to be aligned with their last element
+
+    Returns
+    -------
+        new_imgs: list of nii-like images,
+            Aligned components maps, in the same order as provided
+    """
+    new_imgs = align_many_to_one_nii(masker, imgs[-1], imgs[:-1])
+    new_imgs.append(check_niimg_4d(imgs[-1]))
+    return new_imgs
diff --git a/nilearn_sandbox/tests/__init__.py b/nilearn_sandbox/tests/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/nilearn_sandbox/tests/test_map_alignment.py b/nilearn_sandbox/tests/test_map_alignment.py
new file mode 100644
index 0000000..4d89feb
--- /dev/null
+++ b/nilearn_sandbox/tests/test_map_alignment.py
@@ -0,0 +1,59 @@
+import nibabel
+import numpy as np
+from numpy.testing import assert_array_almost_equal, assert_raises
+from nilearn.input_data import MultiNiftiMasker
+from nilearn_sandbox._utils.map_alignment import align_many_to_one_nii, \
+    align_list_with_last_nii, _align_one_to_one_flat, _align_many_to_one_flat
+
+
+def test_align_many_to_one_nii():
+    affine = np.eye(4)
+    rng = np.random.RandomState(0)
+    a = rng.randn(10, 5 * 5 * 5)
+    b = rng.permutation(a)
+    c = rng.permutation(a)
+    masker = MultiNiftiMasker(mask_img=nibabel.Nifti1Image(np.ones((5, 5, 5)),
+                                                           affine=affine))
+    masker.fit()
+    img_a = masker.inverse_transform(a)
+    img_b = masker.inverse_transform(b)
+    img_c = masker.inverse_transform(c)
+    new_img_b = align_many_to_one_nii(masker, img_a, img_b)
+    new_b = masker.transform(new_img_b)
+    assert_array_almost_equal(a, new_b)
+    results = align_list_with_last_nii(masker, (img_b, img_c, img_a))
+    new_b = masker.transform(results[0])
+    new_c = masker.transform(results[1])
+    assert_array_almost_equal(a, new_b)
+    assert_array_almost_equal(a, new_c)
+
+
+def test_align_one_to_one_flat():
+    rng = np.random.RandomState(0)
+    a = rng.rand(10, 100)
+    a_copy = a.copy()
+    b = rng.permutation(a)
+    b_copy = b.copy()
+    c = _align_one_to_one_flat(a, b, inplace=False)
+    assert_array_almost_equal(a, c)
+    assert_array_almost_equal(a, a_copy)
+    assert_array_almost_equal(b, b_copy)
+    _align_one_to_one_flat(a, b, inplace=True)
+    assert_array_almost_equal(a, b)
+    assert_array_almost_equal(a, a_copy)
+    assert_raises(AssertionError, assert_array_almost_equal, b, b_copy)
+
+
+def test_align_flat():
+    rng = np.random.RandomState(0)
+    ref = rng.rand(10, 100)
+    b = rng.permutation(ref)
+    c = rng.permutation(ref)
+    target_list = [b, c]
+    target_list_copy = [b.copy(), c.copy()]
+    aligned_target_list = _align_many_to_one_flat(ref, target_list,
+                                                  inplace=False)
+    for target, target_copy in zip(target_list, target_list_copy):
+        assert_array_almost_equal(target, target_copy)
+    for target in aligned_target_list:
+        assert_array_almost_equal(ref, target)
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