diff --git a/include/openmc/capi.h b/include/openmc/capi.h
index 9bfe4aa9e..07c6bc80e 100644
--- a/include/openmc/capi.h
+++ b/include/openmc/capi.h
@@ -70,6 +70,7 @@ extern "C" {
   int openmc_next_batch(int* status);
   int openmc_nuclide_name(int index, const char** name);
   int openmc_plot_geometry();
+  int openmc_id_map(void* slice, int32_t *data_out);
   int openmc_reset();
   int openmc_run();
   void openmc_set_seed(int64_t new_seed);
diff --git a/include/openmc/plot.h b/include/openmc/plot.h
index aef7e613b..0bbd3c3ad 100644
--- a/include/openmc/plot.h
+++ b/include/openmc/plot.h
@@ -20,7 +20,7 @@ namespace openmc {
 //===============================================================================
 
 class Plot;
-class PlotC;
+
 
 namespace model {
 
@@ -74,21 +74,16 @@ enum class PlotColorBy {
 //===============================================================================
 // Plot class
 //===============================================================================
-
-
-// plot class for interaction with external code
-class CPlot {
-
-public:
+struct Slice {
+  // Members
   Position origin_; //!< Plot origin in geometry
   Position width_; //!< Plot width in geometry
   PlotBasis basis_; //!< Plot basis (XY/XZ/YZ)
-  std::array<int, 3> pixels_; //!< Plot size in pixels
+  int pixels_[3]; //!< Plot size in pixels
   int level_; //!< Plot universe level
 };
 
-
-class Plot : public CPlot
+class Plot : public Slice
 {
 
 public:
diff --git a/openmc/capi/plot.py b/openmc/capi/plot.py
index 10a6aa280..fe7dd531c 100644
--- a/openmc/capi/plot.py
+++ b/openmc/capi/plot.py
@@ -6,19 +6,18 @@ from .error import _error_handler
 
 import numpy as np
 
-class _IntThree():
-    type_ = c_int*3
-    val_ = None
-    def __init__(self, vals=None):
-        if vals and iterable(vals) and all(vals == int):
-            self.val_ = type_(vals[0], vals[1], vals[2])
-        else:
-            raise ValueError("{} is not a valid object to construct IntThree.".format(vals))
-
-    def __str__(self):
-        return "({}, {}, {})".format(self.val_[0], self.val_[1], self.val_[2])
-
 class _Position(Structure):
+    """Definition of an xyz location in space with underlying c-types
+
+    C-type Attributes
+    -----------------
+    x : c_double
+        Position's x value (default: 0.0)
+    y : c_double
+        Position's y value (default: 0.0)
+    z : c_double
+        Position's z value (default: 0.0)
+    """
     _fields_ = [('x', c_double),
                 ('y', c_double),
                 ('z', c_double)]
@@ -61,9 +60,43 @@ class _Position(Structure):
         self.z = z_val
 
     def __str__(self):
-        return "({}, {}, {})".format(self.x, self.y, self.z)
+        return "Position: ({}, {}, {})".format(self.x, self.y, self.z)
+
 
 class _Plot(Structure):
+    """A Plot structure defining a 2-D slice with underlying c-types
+
+    C-Type Attributes
+    -----------------
+    origin : openmc.capi.plot._Position
+        A position defining the origin of the plot.
+    width_ : openmc.capi.plot._Position
+        The width of the plot along the x, y, and z axes, respectively
+    basis_ : c_int
+        The axes basis of the plot view.
+    pixels_ : c_int[3]
+        The resolution of the plot in the horizontal and vertical dimensions
+    level_ : c_int
+        The universe level for the plot view
+
+    Attributes
+    ----------
+    origin : tuple or list of ndarray
+        Origin (center) of the plot
+    width : float
+        The horizontal dimension of the plot in geometry units (cm)
+    height : float
+        The vertical dimension of the plot in geometry units (cm)
+    basis : string
+        One of {'xy', 'xz', 'yz'} indicating the horizontal and vertical
+        axes of the plot.
+    hRes : float
+        The horizontal resolution of the plot in pixels
+    vRes : float
+        The vertical resolution of the plot in pixels
+    level : int
+        The universe level for the plot (default: -1 -> all universes shown)
+    """
     _fields_ = [('origin_', _Position),
                 ('width_', _Position),
                 ('basis_', c_int),
@@ -127,6 +160,7 @@ class _Plot(Structure):
     def basis(self, basis):
         if isinstance(basis, str):
             valid_bases = ('xy', 'xz', 'yz')
+            basis = basis.lower()
             if basis not in valid_bases:
                 raise ValueError("{} is not a valid plot basis.".format(basis))
 
@@ -159,25 +193,43 @@ class _Plot(Structure):
     def level(self, level):
         self.level_ = level
 
-    def __str__(self):
-        out_str = "-------"
+    def __repr__(self):
+        out_str  = "-----\n"
         out_str += "Plot:\n"
-        out_str += "-------"
-        out_str += "Origin: " + str(self.origin) + "\n"
-        out_str += "Width: " + str(self.width) + "\n"
-        out_str += "Height: " + str(self.height) + "\n"
-        out_str += "Basis: " + str(self.basis) + "\n"
-        out_str += "HRes: " + str(self.hRes) + "\n"
-        out_str += "VRes: " + str(self.vRes) + "\n"
-        out_str += "Level: " + str(self.level) + "\n"
+        out_str += "-----\n"
+        out_str += "Origin: {}\n".format(self.origin)
+        out_str += "Width: {}\n".format(self.width)
+        out_str += "Height: {}\n".format(self.height)
+        out_str += "Basis: {}\n".format(self.basis)
+        out_str += "HRes: {}\n".format(self.hRes)
+        out_str += "VRes: {}\n".format(self.vRes)
+        out_str += "Level: {}\n".format(self.level)
         return out_str
 
+    def __str__(self):
+        return self.__repr__()
+
 
 _dll.openmc_id_map.argtypes= [POINTER(_Plot),]
 _dll.openmc_id_map.restype = c_int
 _dll.openmc_id_map.errcheck = _error_handler
 
+
 def id_map(plot):
-    img_data = np.zeros((plot.pixels_[1], plot.pixels_[0], 2), dtype=np.dtype('int32'))
-    out = _dll.openmc_id_map(POINTER(_Plot)(plot), img_data.ctypes.data_as(POINTER(c_int32)))
+    """
+    Generate a 2-D map of (cell_id, material_id). Used for in-memory image generation.
+
+    Parameters
+    ----------
+    plot : An openmc.capi.plot._Plot object describing the slice of the model to
+           be generated
+
+    Returns
+    -------
+    id_map : a NumPy array with shape (vertical pixels, horizontal pixels, 2)
+             of OpenMC property ids with dtype int32
+
+    """
+    img_data = np.zeros((plot.vRes, plot.hRes, 2), dtype=np.dtype('int32'))
+    _dll.openmc_id_map(POINTER(_Plot)(plot), img_data.ctypes.data_as(POINTER(c_int32)))
     return img_data
diff --git a/src/plot.cpp b/src/plot.cpp
index 9bf3656d9..73aa3d4f6 100644
--- a/src/plot.cpp
+++ b/src/plot.cpp
@@ -886,7 +886,8 @@ void create_voxel(Plot pl)
   // Write current date and time
   write_attribute(file_id, "date_and_time", time_stamp().c_str());
   hsize_t three = 3;
-  write_attribute(file_id, "num_voxels", pl.pixels_);
+  std::array<int, 3> pixels = {pl.pixels_[0], pl.pixels_[1], pl.pixels_[2]};
+  write_attribute(file_id, "num_voxels", pixels);
   write_attribute(file_id, "voxel_width", vox);
   write_attribute(file_id, "lower_left", ll);
 
@@ -979,40 +980,42 @@ RGBColor random_color() {
   return {int(prn()*255), int(prn()*255), int(prn()*255)};
 }
 
-extern "C" int openmc_id_map(const CPlot& pl, int* data_out) {
+extern "C" int openmc_id_map(void* slice, int32_t* data_out) {
 
-  size_t width = pl.pixels_[0];
-  size_t height = pl.pixels_[1];
+  auto* sl = static_cast<Slice*>(slice);
 
-  double in_pixel = (pl.width_[0])/static_cast<double>(width);
-  double out_pixel = (pl.width_[1])/static_cast<double>(height);
+  size_t width = sl->pixels_[0];
+  size_t height = sl->pixels_[1];
+
+  double in_pixel = (sl->width_[0])/static_cast<double>(width);
+  double out_pixel = (sl->width_[1])/static_cast<double>(height);
 
   IDData data;
   data.resize({height, width, 2});
 
   int in_i, out_i;
   double xyz[3];
-  switch(pl.basis_) {
+  switch(sl->basis_) {
   case PlotBasis::xy :
     in_i = 0;
     out_i = 1;
-    xyz[0] = pl.origin_[0] - pl.width_[0] / 2.;
-    xyz[1] = pl.origin_[1] + pl.width_[1] / 2.;
-    xyz[2] = pl.origin_[2];
+    xyz[0] = sl->origin_[0] - sl->width_[0] / 2. + in_pixel / 2.;
+    xyz[1] = sl->origin_[1] + sl->width_[1] / 2. - out_pixel / 2.;
+    xyz[2] = sl->origin_[2];
     break;
   case PlotBasis::xz :
     in_i = 0;
     out_i = 2;
-    xyz[0] = pl.origin_[0] - pl.width_[0] / 2.;
-    xyz[1] = pl.origin_[1];
-    xyz[2] = pl.origin_[2] + pl.width_[1] / 2.;
+    xyz[0] = sl->origin_[0] - sl->width_[0] / 2. + in_pixel / 2.;
+    xyz[1] = sl->origin_[1];
+    xyz[2] = sl->origin_[2] + sl->width_[1] / 2. - out_pixel / 2.;
     break;
   case PlotBasis::yz :
     in_i = 1;
     out_i = 2;
-    xyz[0] = pl.origin_[0];
-    xyz[1] = pl.origin_[1] - pl.width_[0] / 2.;
-    xyz[2] = pl.origin_[2] + pl.width_[1] / 2.;
+    xyz[0] = sl->origin_[0];
+    xyz[1] = sl->origin_[1] - sl->width_[0] / 2. + in_pixel / 2.;
+    xyz[2] = sl->origin_[2] + sl->width_[1] / 2. - out_pixel / 2.;
     break;
   }
 
@@ -1025,15 +1028,15 @@ extern "C" int openmc_id_map(const CPlot& pl, int* data_out) {
   std::copy(xyz, xyz+3, p.coord[0].xyz);
   std::copy(dir, dir+3, p.coord[0].uvw);
   p.coord[0].universe = model::root_universe;
-  int level = pl.level_;
+  int level = sl->level_;
   int j{};
 
 #pragma omp for
   for (int y = 0; y < height; y++) {
     p.coord[0].xyz[out_i] = xyz[out_i] - out_pixel * y;
-    p.n_coord = 1;
     for (int x = 0; x < width; x++) {
       p.coord[0].xyz[in_i] = xyz[in_i] + in_pixel * x;
+      p.n_coord = 1;
       // local variables
       bool found_cell = find_cell(&p, 0);
       j = p.n_coord - 1;
diff --git a/tests/unit_tests/test_capi.py b/tests/unit_tests/test_capi.py
index 0ebc898b4..9d9ab66c0 100644
--- a/tests/unit_tests/test_capi.py
+++ b/tests/unit_tests/test_capi.py
@@ -400,3 +400,24 @@ def test_load_nuclide(capi_init):
     # load non-existent nuclide
     with pytest.raises(exc.DataError):
         openmc.capi.load_nuclide('Pu3')
+
+
+def test_id_map(capi_init):
+    expected_ids = np.array([[(3,3), (2,2), (3,3)],
+                             [(2,2), (1,1), (2,2)],
+                             [(3,3), (2,2), (3,3)]], dtype = 'int32')
+
+    # create a plot object
+    p = openmc.capi.plot._Plot()
+
+    p.width = 1.26
+    p.height = 1.26
+    p.vRes = 3
+    p.hRes = 3
+    p.origin = (0,0,0)
+    p.basis = 'xy'
+    p.level = -1
+
+    ids = openmc.capi.plot.id_map(p)
+    print(ids)
+    assert np.array_equal(expected_ids, ids)