diff --git a/masque/builder/devices.py b/masque/builder/devices.py
index 54d3940..2bccfb1 100644
--- a/masque/builder/devices.py
+++ b/masque/builder/devices.py
@@ -14,8 +14,9 @@ from numpy.typing import ArrayLike, NDArray
 from ..pattern import Pattern
 from ..subpattern import SubPattern
 from ..traits import PositionableImpl, Rotatable, PivotableImpl, Copyable, Mirrorable
-from ..utils import AutoSlots, rotation_matrix_2d
+from ..utils import AutoSlots
 from ..error import DeviceError
+from ..ports import PortList, Port
 from .tools import Tool
 from .utils import ell
 
@@ -23,382 +24,10 @@ from .utils import ell
 logger = logging.getLogger(__name__)
 
 
-P = TypeVar('P', bound='Port')
-PL  = TypeVar('PL',  bound='PortList')
-PL2 = TypeVar('PL2', bound='PortList')
 D  = TypeVar('D',  bound='Device')
 DR  = TypeVar('DR',  bound='DeviceRef')
 
 
-class Port(PositionableImpl, Rotatable, PivotableImpl, Copyable, Mirrorable, metaclass=AutoSlots):
-    """
-    A point at which a `Device` can be snapped to another `Device`.
-
-    Each port has an `offset` ((x, y) position) and may also have a
-      `rotation` (orientation) and a `ptype` (port type).
-
-    The `rotation` is an angle, in radians, measured counterclockwise
-      from the +x axis, pointing inwards into the device which owns the port.
-      The rotation may be set to `None`, indicating that any orientation is
-      allowed (e.g. for a DC electrical port). It is stored modulo 2pi.
-
-    The `ptype` is an arbitrary string, default of `unk` (unknown).
-    """
-    __slots__ = ('ptype', '_rotation')
-
-    _rotation: Optional[float]
-    """ radians counterclockwise from +x, pointing into device body.
-        Can be `None` to signify undirected port """
-
-    ptype: str
-    """ Port types must match to be plugged together if both are non-zero """
-
-    def __init__(
-            self,
-            offset: ArrayLike,
-            rotation: Optional[float],
-            ptype: str = 'unk',
-            ) -> None:
-        self.offset = offset
-        self.rotation = rotation
-        self.ptype = ptype
-
-    @property
-    def rotation(self) -> Optional[float]:
-        """ Rotation, radians counterclockwise, pointing into device body. Can be None. """
-        return self._rotation
-
-    @rotation.setter
-    def rotation(self, val: float) -> None:
-        if val is None:
-            self._rotation = None
-        else:
-            if not numpy.size(val) == 1:
-                raise DeviceError('Rotation must be a scalar')
-            self._rotation = val % (2 * pi)
-
-    def get_bounds(self):
-        return numpy.vstack((self.offset, self.offset))
-
-    def set_ptype(self: P, ptype: str) -> P:
-        """ Chainable setter for `ptype` """
-        self.ptype = ptype
-        return self
-
-    def mirror(self: P, axis: int) -> P:
-        self.offset[1 - axis] *= -1
-        if self.rotation is not None:
-            self.rotation *= -1
-            self.rotation += axis * pi
-        return self
-
-    def rotate(self: P, rotation: float) -> P:
-        if self.rotation is not None:
-            self.rotation += rotation
-        return self
-
-    def set_rotation(self: P, rotation: Optional[float]) -> P:
-        self.rotation = rotation
-        return self
-
-    def __repr__(self) -> str:
-        if self.rotation is None:
-            rot = 'any'
-        else:
-            rot = str(numpy.rad2deg(self.rotation))
-        return f'<{self.offset}, {rot}, [{self.ptype}]>'
-
-
-class PortList(Copyable, Mirrorable, metaclass=ABCMeta):
-    __slots__ = ('ports',)
-
-    ports: Dict[str, Port]
-    """ Uniquely-named ports which can be used to snap to other Device instances"""
-
-    @overload
-    def __getitem__(self, key: str) -> Port:
-        pass
-
-    @overload
-    def __getitem__(self, key: Union[List[str], Tuple[str, ...], KeysView[str], ValuesView[str]]) -> Dict[str, Port]:
-        pass
-
-    def __getitem__(self, key: Union[str, Iterable[str]]) -> Union[Port, Dict[str, Port]]:
-        """
-        For convenience, ports can be read out using square brackets:
-        - `device['A'] == Port((0, 0), 0)`
-        - `device[['A', 'B']] == {'A': Port((0, 0), 0),
-                                  'B': Port((0, 0), pi)}`
-        """
-        if isinstance(key, str):
-            return self.ports[key]
-        else:
-            return {k: self.ports[k] for k in key}
-
-    def rename_ports(
-            self: PL,
-            mapping: Dict[str, Optional[str]],
-            overwrite: bool = False,
-            ) -> PL:
-        """
-        Renames ports as specified by `mapping`.
-        Ports can be explicitly deleted by mapping them to `None`.
-
-        Args:
-            mapping: Dict of `{'old_name': 'new_name'}` pairs. Names can be mapped
-                to `None` to perform an explicit deletion. `'new_name'` can also
-                overwrite an existing non-renamed port to implicitly delete it if
-                `overwrite` is set to `True`.
-            overwrite: Allows implicit deletion of ports if set to `True`; see `mapping`.
-
-        Returns:
-            self
-        """
-        if not overwrite:
-            duplicates = (set(self.ports.keys()) - set(mapping.keys())) & set(mapping.values())
-            if duplicates:
-                raise DeviceError(f'Unrenamed ports would be overwritten: {duplicates}')
-
-        renamed = {mapping[k]: self.ports.pop(k) for k in mapping.keys()}
-        if None in renamed:
-            del renamed[None]
-
-        self.ports.update(renamed)      # type: ignore
-        return self
-
-    def check_ports(
-            self: PL,
-            other_names: Iterable[str],
-            map_in: Optional[Dict[str, str]] = None,
-            map_out: Optional[Dict[str, Optional[str]]] = None,
-            ) -> PL:
-        """
-        Given the provided port mappings, check that:
-            - All of the ports specified in the mappings exist
-            - There are no duplicate port names after all the mappings are performed
-
-        Args:
-            other_names: List of port names being considered for inclusion into
-                `self.ports` (before mapping)
-            map_in: Dict of `{'self_port': 'other_port'}` mappings, specifying
-                port connections between the two devices.
-            map_out: Dict of `{'old_name': 'new_name'}` mappings, specifying
-                new names for unconnected `other_names` ports.
-
-        Returns:
-            self
-
-        Raises:
-            `DeviceError` if any ports specified in `map_in` or `map_out` do not
-                exist in `self.ports` or `other_names`.
-            `DeviceError` if there are any duplicate names after `map_in` and `map_out`
-                are applied.
-        """
-        if map_in is None:
-            map_in = {}
-
-        if map_out is None:
-            map_out = {}
-
-        other = set(other_names)
-
-        missing_inkeys = set(map_in.keys()) - set(self.ports.keys())
-        if missing_inkeys:
-            raise DeviceError(f'`map_in` keys not present in device: {missing_inkeys}')
-
-        missing_invals = set(map_in.values()) - other
-        if missing_invals:
-            raise DeviceError(f'`map_in` values not present in other device: {missing_invals}')
-
-        missing_outkeys = set(map_out.keys()) - other
-        if missing_outkeys:
-            raise DeviceError(f'`map_out` keys not present in other device: {missing_outkeys}')
-
-        orig_remaining = set(self.ports.keys()) - set(map_in.keys())
-        other_remaining = other - set(map_out.keys()) - set(map_in.values())
-        mapped_vals = set(map_out.values())
-        mapped_vals.discard(None)
-
-        conflicts_final = orig_remaining & (other_remaining | mapped_vals)
-        if conflicts_final:
-            raise DeviceError(f'Device ports conflict with existing ports: {conflicts_final}')
-
-        conflicts_partial = other_remaining & mapped_vals
-        if conflicts_partial:
-            raise DeviceError(f'`map_out` targets conflict with non-mapped outputs: {conflicts_partial}')
-
-        map_out_counts = Counter(map_out.values())
-        map_out_counts[None] = 0
-        conflicts_out = {k for k, v in map_out_counts.items() if v > 1}
-        if conflicts_out:
-            raise DeviceError(f'Duplicate targets in `map_out`: {conflicts_out}')
-
-        return self
-
-    def as_interface(
-            self,
-            in_prefix: str = 'in_',
-            out_prefix: str = '',
-            port_map: Optional[Union[Dict[str, str], Sequence[str]]] = None
-            ) -> 'Device':
-        """
-        Begin building a new device based on all or some of the ports in the
-          current device. Do not include the current device; instead use it
-          to define ports (the "interface") for the new device.
-
-        The ports specified by `port_map` (default: all ports) are copied to
-          new device, and additional (input) ports are created facing in the
-          opposite directions. The specified `in_prefix` and `out_prefix` are
-          prepended to the port names to differentiate them.
-
-        By default, the flipped ports are given an 'in_' prefix and unflipped
-          ports keep their original names, enabling intuitive construction of
-          a device that will "plug into" the current device; the 'in_*' ports
-          are used for plugging the devices together while the original port
-          names are used for building the new device.
-
-        Another use-case could be to build the new device using the 'in_'
-          ports, creating a new device which could be used in place of the
-          current device.
-
-        Args:
-            in_prefix: Prepended to port names for newly-created ports with
-                reversed directions compared to the current device.
-            out_prefix: Prepended to port names for ports which are directly
-                copied from the current device.
-            port_map: Specification for ports to copy into the new device:
-                - If `None`, all ports are copied.
-                - If a sequence, only the listed ports are copied
-                - If a mapping, the listed ports (keys) are copied and
-                    renamed (to the values).
-
-        Returns:
-            The new device, with an empty pattern and 2x as many ports as
-              listed in port_map.
-
-        Raises:
-            `DeviceError` if `port_map` contains port names not present in the
-                current device.
-            `DeviceError` if applying the prefixes results in duplicate port
-                names.
-        """
-        if port_map:
-            if isinstance(port_map, dict):
-                missing_inkeys = set(port_map.keys()) - set(self.ports.keys())
-                orig_ports = {port_map[k]: v for k, v in self.ports.items() if k in port_map}
-            else:
-                port_set = set(port_map)
-                missing_inkeys = port_set - set(self.ports.keys())
-                orig_ports = {k: v for k, v in self.ports.items() if k in port_set}
-
-            if missing_inkeys:
-                raise DeviceError(f'`port_map` keys not present in device: {missing_inkeys}')
-        else:
-            orig_ports = self.ports
-
-        ports_in = {f'{in_prefix}{name}': port.deepcopy().rotate(pi)
-                    for name, port in orig_ports.items()}
-        ports_out = {f'{out_prefix}{name}': port.deepcopy()
-                    for name, port in orig_ports.items()}
-
-        duplicates = set(ports_out.keys()) & set(ports_in.keys())
-        if duplicates:
-            raise DeviceError(f'Duplicate keys after prefixing, try a different prefix: {duplicates}')
-
-        new = Device(ports={**ports_in, **ports_out})
-        return new
-
-    def find_transform(
-            self: PL,
-            other: PL2,
-            map_in: Dict[str, str],
-            *,
-            mirrored: Tuple[bool, bool] = (False, False),
-            set_rotation: Optional[bool] = None,
-            ) -> Tuple[NDArray[numpy.float64], float, NDArray[numpy.float64]]:
-        """
-        Given a device `other` and a mapping `map_in` specifying port connections,
-          find the transform which will correctly align the specified ports.
-
-        Args:
-            other: a device
-            map_in: Dict of `{'self_port': 'other_port'}` mappings, specifying
-                port connections between the two devices.
-            mirrored: Mirrors `other` across the x or y axes prior to
-                connecting any ports.
-            set_rotation: If the necessary rotation cannot be determined from
-                the ports being connected (i.e. all pairs have at least one
-                port with `rotation=None`), `set_rotation` must be provided
-                to indicate how much `other` should be rotated. Otherwise,
-                `set_rotation` must remain `None`.
-
-        Returns:
-            - The (x, y) translation (performed last)
-            - The rotation (radians, counterclockwise)
-            - The (x, y) pivot point for the rotation
-
-            The rotation should be performed before the translation.
-        """
-        s_ports = self[map_in.keys()]
-        o_ports = other[map_in.values()]
-
-        s_offsets = numpy.array([p.offset for p in s_ports.values()])
-        o_offsets = numpy.array([p.offset for p in o_ports.values()])
-        s_types = [p.ptype for p in s_ports.values()]
-        o_types = [p.ptype for p in o_ports.values()]
-
-        s_rotations = numpy.array([p.rotation if p.rotation is not None else 0 for p in s_ports.values()])
-        o_rotations = numpy.array([p.rotation if p.rotation is not None else 0 for p in o_ports.values()])
-        s_has_rot = numpy.array([p.rotation is not None for p in s_ports.values()], dtype=bool)
-        o_has_rot = numpy.array([p.rotation is not None for p in o_ports.values()], dtype=bool)
-        has_rot = s_has_rot & o_has_rot
-
-        if mirrored[0]:
-            o_offsets[:, 1] *= -1
-            o_rotations *= -1
-        if mirrored[1]:
-            o_offsets[:, 0] *= -1
-            o_rotations *= -1
-            o_rotations += pi
-
-        type_conflicts = numpy.array([st != ot and st != 'unk' and ot != 'unk'
-                                      for st, ot in zip(s_types, o_types)])
-        if type_conflicts.any():
-            ports = numpy.where(type_conflicts)
-            msg = 'Ports have conflicting types:\n'
-            for nn, (k, v) in enumerate(map_in.items()):
-                if type_conflicts[nn]:
-                    msg += f'{k} | {s_types[nn]}:{o_types[nn]} | {v}\n'
-            msg = ''.join(traceback.format_stack()) + '\n' + msg
-            warnings.warn(msg, stacklevel=2)
-
-        rotations = numpy.mod(s_rotations - o_rotations - pi, 2 * pi)
-        if not has_rot.any():
-            if set_rotation is None:
-                DeviceError('Must provide set_rotation if rotation is indeterminate')
-            rotations[:] = set_rotation
-        else:
-            rotations[~has_rot] = rotations[has_rot][0]
-
-        if not numpy.allclose(rotations[:1], rotations):
-            rot_deg = numpy.rad2deg(rotations)
-            msg = f'Port orientations do not match:\n'
-            for nn, (k, v) in enumerate(map_in.items()):
-                msg += f'{k} | {rot_deg[nn]:g} | {v}\n'
-            raise DeviceError(msg)
-
-        pivot = o_offsets[0].copy()
-        rotate_offsets_around(o_offsets, pivot, rotations[0])
-        translations = s_offsets - o_offsets
-        if not numpy.allclose(translations[:1], translations):
-            msg = f'Port translations do not match:\n'
-            for nn, (k, v) in enumerate(map_in.items()):
-                msg += f'{k} | {translations[nn]} | {v}\n'
-            raise DeviceError(msg)
-
-        return translations[0], rotations[0], o_offsets[0]
-
-
 class DeviceRef(PortList):
     __slots__ = ('name',)
 
@@ -908,12 +537,3 @@ class Device(PortList):
     # TODO def path_join() and def bus_join()?
 
 
-def rotate_offsets_around(
-        offsets: NDArray[numpy.float64],
-        pivot: NDArray[numpy.float64],
-        angle: float,
-        ) -> NDArray[numpy.float64]:
-    offsets -= pivot
-    offsets[:] = (rotation_matrix_2d(angle) @ offsets.T).T
-    offsets += pivot
-    return offsets
diff --git a/masque/file/oasis.py b/masque/file/oasis.py
index d3acd7b..4d58d8b 100644
--- a/masque/file/oasis.py
+++ b/masque/file/oasis.py
@@ -11,7 +11,7 @@ Note that OASIS references follow the same convention as `masque`,
   Scaling, rotation, and mirroring apply to individual instances, not grid
    vectors or offsets.
 """
-from typing import List, Any, Dict, Tuple, Callable, Union, Sequence, Iterable, Mapping, Optional
+from typing import List, Any, Dict, Tuple, Callable, Union, Sequence, Iterable, Mapping, Optional, cast
 import re
 import io
 import copy
@@ -479,7 +479,7 @@ def _mlayer2oas(mlayer: layer_t) -> Tuple[int, int]:
 
 def _placement_to_subpat(placement: fatrec.Placement, lib: fatamorgana.OasisLayout) -> SubPattern:
     """
-    Helper function to create a SubPattern from a placment. Sets subpat.target to the placemen name.
+    Helper function to create a SubPattern from a placment. Sets subpat.target to the placement name.
     """
     assert(not isinstance(placement.repetition, fatamorgana.ReuseRepetition))
     xy = numpy.array((placement.x, placement.y))
@@ -548,7 +548,7 @@ def _shapes_to_elements(
             circle = fatrec.Circle(
                 layer=layer,
                 datatype=datatype,
-                radius=radius,
+                radius=cast(int, radius),
                 x=offset[0],
                 y=offset[1],
                 properties=properties,
@@ -565,8 +565,8 @@ def _shapes_to_elements(
             path = fatrec.Path(
                 layer=layer,
                 datatype=datatype,
-                point_list=deltas,
-                half_width=half_width,
+                point_list=cast(Sequence[Sequence[int]], deltas),
+                half_width=cast(int, half_width),
                 x=xy[0],
                 y=xy[1],
                 extension_start=extension_start,       # TODO implement multiple cap types?
@@ -584,7 +584,7 @@ def _shapes_to_elements(
                     datatype=datatype,
                     x=xy[0],
                     y=xy[1],
-                    point_list=points,
+                    point_list=cast(List[List[int]], points),
                     properties=properties,
                     repetition=repetition,
                     ))
@@ -671,16 +671,16 @@ def repetition_masq2fata(
         a_count = rint_cast(rep.a_count)
         b_count = rint_cast(rep.b_count) if rep.b_count is not None else None
         frep = fatamorgana.GridRepetition(
-            a_vector=a_vector,
-            b_vector=b_vector,
-            a_count=a_count,
-            b_count=b_count,
+            a_vector=cast(List[int], a_vector),
+            b_vector=cast(Optional[List[int]], b_vector),
+            a_count=cast(int, a_count),
+            b_count=cast(Optional[int], b_count),
             )
         offset = (0, 0)
     elif isinstance(rep, Arbitrary):
         diffs = numpy.diff(rep.displacements, axis=0)
         diff_ints = rint_cast(diffs)
-        frep = fatamorgana.ArbitraryRepetition(diff_ints[:, 0], diff_ints[:, 1])
+        frep = fatamorgana.ArbitraryRepetition(diff_ints[:, 0], diff_ints[:, 1])        # type: ignore
         offset = rep.displacements[0, :]
     else:
         assert(rep is None)
diff --git a/masque/pattern.py b/masque/pattern.py
index 156c436..81c9748 100644
--- a/masque/pattern.py
+++ b/masque/pattern.py
@@ -18,19 +18,19 @@ from .shapes import Shape, Polygon
 from .label import Label
 from .utils import rotation_matrix_2d, normalize_mirror, AutoSlots, annotations_t
 from .error import PatternError
-from .traits import AnnotatableImpl, Scalable, Mirrorable
-from .traits import Rotatable, Positionable
+from .traits import AnnotatableImpl, Scalable, Mirrorable, Rotatable, Positionable, Repeatable
+from .ports import Port, PortList
 
 
 P = TypeVar('P', bound='Pattern')
 
 
-class Pattern(AnnotatableImpl, Mirrorable, metaclass=AutoSlots):
+class Pattern(PortList, AnnotatableImpl, Mirrorable, metaclass=AutoSlots):
     """
     2D layout consisting of some set of shapes, labels, and references to other Pattern objects
      (via SubPattern). Shapes are assumed to inherit from masque.shapes.Shape or provide equivalent functions.
     """
-    __slots__ = ('shapes', 'labels', 'subpatterns')
+    __slots__ = ('shapes', 'labels', 'subpatterns', 'ports')
 
     shapes: List[Shape]
     """ List of all shapes in this Pattern.
@@ -46,6 +46,9 @@ class Pattern(AnnotatableImpl, Mirrorable, metaclass=AutoSlots):
       (i.e. multiple instances of the same object).
     """
 
+    ports: Dict[str, Port]
+    """ Uniquely-named ports which can be used to snap to other Pattern instances"""
+
     def __init__(
             self,
             *,
@@ -53,6 +56,7 @@ class Pattern(AnnotatableImpl, Mirrorable, metaclass=AutoSlots):
             labels: Sequence[Label] = (),
             subpatterns: Sequence[SubPattern] = (),
             annotations: Optional[annotations_t] = None,
+            ports: Optional[Mapping[str, Port]] = None
             ) -> None:
         """
         Basic init; arguments get assigned to member variables.
@@ -62,6 +66,8 @@ class Pattern(AnnotatableImpl, Mirrorable, metaclass=AutoSlots):
             shapes: Initial shapes in the Pattern
             labels: Initial labels in the Pattern
             subpatterns: Initial subpatterns in the Pattern
+            annotations: Initial annotations for the pattern
+            ports: Any ports in the pattern
         """
         if isinstance(shapes, list):
             self.shapes = shapes
@@ -78,14 +84,25 @@ class Pattern(AnnotatableImpl, Mirrorable, metaclass=AutoSlots):
         else:
             self.subpatterns = list(subpatterns)
 
+        if ports is not None:
+            ports = dict(copy.deepcopy(ports))
+
         self.annotations = annotations if annotations is not None else {}
 
+    def __repr__(self) -> str:
+        s = f'<Pattern: sh{len(self.shapes)} sp{len(self.subpatterns)} la{len(self.labels)} ['
+        for name, port in self.ports.items():
+            s += f'\n\t{name}: {port}'
+        s += ']>'
+        return s
+
     def __copy__(self) -> 'Pattern':
         return Pattern(
             shapes=copy.deepcopy(self.shapes),
             labels=copy.deepcopy(self.labels),
             subpatterns=[copy.copy(sp) for sp in self.subpatterns],
             annotations=copy.deepcopy(self.annotations),
+            ports=copy.deepcopy(self.ports),
             )
 
     def __deepcopy__(self, memo: Optional[Dict] = None) -> 'Pattern':
@@ -95,10 +112,11 @@ class Pattern(AnnotatableImpl, Mirrorable, metaclass=AutoSlots):
             labels=copy.deepcopy(self.labels, memo),
             subpatterns=copy.deepcopy(self.subpatterns, memo),
             annotations=copy.deepcopy(self.annotations, memo),
+            ports=copy.deepcopy(self.ports),
             )
         return new
 
-    def append(self: P, other_pattern: P) -> P:
+    def append(self: P, other_pattern: Pattern) -> P:
         """
         Appends all shapes, labels and subpatterns from other_pattern to self's shapes,
           labels, and supbatterns.
@@ -112,6 +130,8 @@ class Pattern(AnnotatableImpl, Mirrorable, metaclass=AutoSlots):
         self.subpatterns += other_pattern.subpatterns
         self.shapes += other_pattern.shapes
         self.labels += other_pattern.labels
+        self.annotations += other_pattern.annotations
+        self.ports += other_pattern.ports
         return self
 
     def subset(
@@ -119,31 +139,55 @@ class Pattern(AnnotatableImpl, Mirrorable, metaclass=AutoSlots):
             shapes: Optional[Callable[[Shape], bool]] = None,
             labels: Optional[Callable[[Label], bool]] = None,
             subpatterns: Optional[Callable[[SubPattern], bool]] = None,
+            annotations: Optional[Callable[[annotation_t], bool]] = None,
+            ports: Optional[Callable[[str], bool]] = None,
+            default_keep: bool = False
             ) -> 'Pattern':
         """
         Returns a Pattern containing only the entities (e.g. shapes) for which the
           given entity_func returns True.
-        Self is _not_ altered, but shapes, labels, and subpatterns are _not_ copied.
+        Self is _not_ altered, but shapes, labels, and subpatterns are _not_ copied, just referenced.
 
         Args:
-            shapes: Given a shape, returns a boolean denoting whether the shape is a member
-                of the subset. Default always returns False.
-            labels: Given a label, returns a boolean denoting whether the label is a member
-                of the subset. Default always returns False.
-            subpatterns: Given a subpattern, returns a boolean denoting if it is a member
-                of the subset. Default always returns False.
+            shapes: Given a shape, returns a boolean denoting whether the shape is a member of the subset.
+            labels: Given a label, returns a boolean denoting whether the label is a member of the subset.
+            subpatterns: Given a subpattern, returns a boolean denoting if it is a member of the subset.
+            annotations: Given an annotation, returns a boolean denoting if it is a member of the subset.
+            ports: Given a port, returns a boolean denoting if it is a member of the subset.
+            default_keep: If `True`, keeps all elements of a given type if no function is supplied.
+                Default `False` (discards all elements).
 
         Returns:
             A Pattern containing all the shapes and subpatterns for which the parameter
                 functions return True
         """
         pat = Pattern()
+
         if shapes is not None:
             pat.shapes = [s for s in self.shapes if shapes(s)]
+        elif default_keep:
+            pat.shapes = copy.copy(self.shapes)
+
         if labels is not None:
             pat.labels = [s for s in self.labels if labels(s)]
+        elif default_keep:
+            pat.labels = copy.copy(self.labels)
+
         if subpatterns is not None:
             pat.subpatterns = [s for s in self.subpatterns if subpatterns(s)]
+        elif default_keep:
+            pat.subpatterns = copy.copy(self.subpatterns)
+
+        if annotations is not None:
+            pat.annotations = [s for s in self.annotations if annotations(s)]
+        elif default_keep:
+            pat.annotations = copy.copy(self.annotations)
+
+        if ports is not None:
+            pat.ports = {k: v for k, v in self.ports.items() if ports(k)}
+        elif default_keep:
+            pat.ports = copy.copy(self.ports)
+
         return pat
 
     def polygonize(
@@ -281,8 +325,8 @@ class Pattern(AnnotatableImpl, Mirrorable, metaclass=AutoSlots):
         Returns:
             self
         """
-        for entry in chain(self.shapes, self.subpatterns, self.labels):
-            entry.translate(offset)
+        for entry in chain(self.shapes, self.subpatterns, self.labels, self.ports):
+            cast(Positionable, entry).translate(offset)
         return self
 
     def scale_elements(self: P, c: float) -> P:
@@ -295,9 +339,8 @@ class Pattern(AnnotatableImpl, Mirrorable, metaclass=AutoSlots):
         Returns:
             self
         """
-        entry: Scalable
         for entry in chain(self.shapes, self.subpatterns):
-            entry.scale_by(c)
+            cast(Scalable, entry).scale_by(c)
         return self
 
     def scale_by(self: P, c: float) -> P:
@@ -311,16 +354,23 @@ class Pattern(AnnotatableImpl, Mirrorable, metaclass=AutoSlots):
         Returns:
             self
         """
-        entry: Scalable
         for entry in chain(self.shapes, self.subpatterns):
-            entry.offset *= c
-            entry.scale_by(c)
-            if entry.repetition:
-                entry.repetition.scale_by(c)
+            cast(Positionable, entry).offset *= c
+            cast(Scalable, entry).scale_by(c)
+
+            rep = cast(Repeatable, entry).repetition
+            if rep:
+                rep.scale_by(c)
+
         for label in self.labels:
-            label.offset *= c
-            if label.repetition:
-                label.repetition.scale_by(c)
+            cast(Positionable, label).offset *= c
+
+            rep = cast(Repeatable, label).repetition
+            if rep:
+                rep.scale_by(c)
+
+        for port in self.ports.values():
+            port.offset *= c
         return self
 
     def rotate_around(self: P, pivot: ArrayLike, rotation: float) -> P:
@@ -351,8 +401,9 @@ class Pattern(AnnotatableImpl, Mirrorable, metaclass=AutoSlots):
         Returns:
             self
         """
-        for entry in chain(self.shapes, self.subpatterns, self.labels):
-            entry.offset = numpy.dot(rotation_matrix_2d(rotation), entry.offset)
+        for entry in chain(self.shapes, self.subpatterns, self.labels, self.ports):
+            old_offset = cast(Positionable, entry).offset
+            cast(Positionable, entry).offset = numpy.dot(rotation_matrix_2d(rotation), old_offset)
         return self
 
     def rotate_elements(self: P, rotation: float) -> P:
@@ -380,8 +431,8 @@ class Pattern(AnnotatableImpl, Mirrorable, metaclass=AutoSlots):
         Returns:
             self
         """
-        for entry in chain(self.shapes, self.subpatterns, self.labels):
-            entry.offset[axis - 1] *= -1
+        for entry in chain(self.shapes, self.subpatterns, self.labels, self.ports):
+            cast(Positionable, entry).offset[axis - 1] *= -1
         return self
 
     def mirror_elements(self: P, axis: int) -> P:
@@ -566,6 +617,3 @@ class Pattern(AnnotatableImpl, Mirrorable, metaclass=AutoSlots):
             pyplot.xlabel('x')
             pyplot.ylabel('y')
             pyplot.show()
-
-    def __repr__(self) -> str:
-        return (f'<Pattern: sh{len(self.shapes)} sp{len(self.subpatterns)} la{len(self.labels)}>')
diff --git a/masque/repetition.py b/masque/repetition.py
index f7842c0..02d3c96 100644
--- a/masque/repetition.py
+++ b/masque/repetition.py
@@ -39,10 +39,10 @@ class Grid(Repetition, metaclass=AutoSlots):
 
     Note that the offsets in either the 2D or 1D grids do not have to be axis-aligned.
     """
-    __slots__ = ('_a_vector',
-                 '_b_vector',
-                 '_a_count',
-                 '_b_count')
+    __slots__ = (
+        '_a_vector','_b_vector',
+        '_a_count', '_b_count',
+        )
 
     _a_vector: NDArray[numpy.float64]
     """ Vector `[x, y]` specifying the first lattice vector of the grid.
diff --git a/masque/shapes/arc.py b/masque/shapes/arc.py
index b33427e..c5712e5 100644
--- a/masque/shapes/arc.py
+++ b/masque/shapes/arc.py
@@ -21,8 +21,12 @@ class Arc(Shape, metaclass=AutoSlots):
     The rotation gives the angle from x-axis, counterclockwise, to the first (x) radius.
     The start and stop angle are measured counterclockwise from the first (x) radius.
     """
-    __slots__ = ('_radii', '_angles', '_width', '_rotation',
-                 'poly_num_points', 'poly_max_arclen')
+    __slots__ = (
+        '_radii', '_angles', '_width', '_rotation',
+        'poly_num_points', 'poly_max_arclen',
+        # Inherited
+        '_offset', '_layer', '_repetition', '_annotations',
+        )
 
     _radii: NDArray[numpy.float64]
     """ Two radii for defining an ellipse """
diff --git a/masque/shapes/circle.py b/masque/shapes/circle.py
index 7854044..e1b0bf2 100644
--- a/masque/shapes/circle.py
+++ b/masque/shapes/circle.py
@@ -15,7 +15,11 @@ class Circle(Shape, metaclass=AutoSlots):
     """
     A circle, which has a position and radius.
     """
-    __slots__ = ('_radius', 'poly_num_points', 'poly_max_arclen')
+    __slots__ = (
+        '_radius', 'poly_num_points', 'poly_max_arclen',
+        # Inherited
+        '_offset', '_layer', '_repetition', '_annotations',
+        )
 
     _radius: float
     """ Circle radius """
diff --git a/masque/shapes/ellipse.py b/masque/shapes/ellipse.py
index 5cd532e..2d21b86 100644
--- a/masque/shapes/ellipse.py
+++ b/masque/shapes/ellipse.py
@@ -17,8 +17,12 @@ class Ellipse(Shape, metaclass=AutoSlots):
     An ellipse, which has a position, two radii, and a rotation.
     The rotation gives the angle from x-axis, counterclockwise, to the first (x) radius.
     """
-    __slots__ = ('_radii', '_rotation',
-                 'poly_num_points', 'poly_max_arclen')
+    __slots__ = (
+        '_radii', '_rotation',
+        'poly_num_points', 'poly_max_arclen',
+        # Inherited
+        '_offset', '_layer', '_repetition', '_annotations',
+        )
 
     _radii: NDArray[numpy.float64]
     """ Ellipse radii """
diff --git a/masque/shapes/path.py b/masque/shapes/path.py
index dafe523..f177d07 100644
--- a/masque/shapes/path.py
+++ b/masque/shapes/path.py
@@ -28,7 +28,11 @@ class Path(Shape, metaclass=AutoSlots):
 
     A normalized_form(...) is available, but can be quite slow with lots of vertices.
     """
-    __slots__ = ('_vertices', '_width', '_cap', '_cap_extensions')
+    __slots__ = (
+        '_vertices', '_width', '_cap', '_cap_extensions',
+        # Inherited
+        '_offset', '_layer', '_repetition', '_annotations',
+        )
     _vertices: NDArray[numpy.float64]
     _width: float
     _cap: PathCap
diff --git a/masque/shapes/polygon.py b/masque/shapes/polygon.py
index 20d5b47..0a05e78 100644
--- a/masque/shapes/polygon.py
+++ b/masque/shapes/polygon.py
@@ -19,7 +19,11 @@ class Polygon(Shape, metaclass=AutoSlots):
 
     A `normalized_form(...)` is available, but can be quite slow with lots of vertices.
     """
-    __slots__ = ('_vertices',)
+    __slots__ = (
+        '_vertices',
+        # Inherited
+        '_offset', '_layer', '_repetition', '_annotations',
+        )
 
     _vertices: NDArray[numpy.float64]
     """ Nx2 ndarray of vertices `[[x0, y0], [x1, y1], ...]` """
diff --git a/masque/shapes/shape.py b/masque/shapes/shape.py
index 66f83db..3e4c1bb 100644
--- a/masque/shapes/shape.py
+++ b/masque/shapes/shape.py
@@ -17,7 +17,7 @@ if TYPE_CHECKING:
 # Type definitions
 normalized_shape_tuple = Tuple[
     Tuple,
-    Tuple[NDArray[numpy.float64], float, float, bool, float],
+    Tuple[NDArray[numpy.float64], float, float, bool],
     Callable[[], 'Shape'],
     ]
 
diff --git a/masque/shapes/text.py b/masque/shapes/text.py
index 9fad29a..92ecb68 100644
--- a/masque/shapes/text.py
+++ b/masque/shapes/text.py
@@ -22,7 +22,11 @@ class Text(RotatableImpl, Shape, metaclass=AutoSlots):
     Text (to be printed e.g. as a set of polygons).
     This is distinct from non-printed Label objects.
     """
-    __slots__ = ('_string', '_height', '_mirrored', 'font_path')
+    __slots__ = (
+        '_string', '_height', '_mirrored', 'font_path',
+        # Inherited
+        '_offset', '_layer', '_repetition', '_annotations', '_rotation',
+        )
 
     _string: str
     _height: float
diff --git a/masque/traits/positionable.py b/masque/traits/positionable.py
index f4d1a5f..b7548cb 100644
--- a/masque/traits/positionable.py
+++ b/masque/traits/positionable.py
@@ -30,10 +30,10 @@ class Positionable(metaclass=ABCMeta):
         """
         pass
 
-#    @offset.setter
-#    @abstractmethod
-#    def offset(self, val: ArrayLike):
-#        pass
+    @offset.setter
+    @abstractmethod
+    def offset(self, val: ArrayLike):
+        pass
 
     @abstractmethod
     def set_offset(self: T, offset: ArrayLike) -> T:
diff --git a/masque/utils/__init__.py b/masque/utils/__init__.py
index eb0741a..d55d9b2 100644
--- a/masque/utils/__init__.py
+++ b/masque/utils/__init__.py
@@ -11,6 +11,6 @@ from .bitwise import get_bit, set_bit
 from .vertices import (
     remove_duplicate_vertices, remove_colinear_vertices, poly_contains_points
     )
-from .transform import rotation_matrix_2d, normalize_mirror
+from .transform import rotation_matrix_2d, normalize_mirror, rotate_offsets_around
 
 #from . import pack2d
diff --git a/masque/utils/transform.py b/masque/utils/transform.py
index 92f52c5..6265d26 100644
--- a/masque/utils/transform.py
+++ b/masque/utils/transform.py
@@ -38,3 +38,17 @@ def normalize_mirror(mirrored: Sequence[bool]) -> Tuple[bool, float]:
     mirror_x = (mirrored_x != mirrored_y)  # XOR
     angle = numpy.pi if mirrored_y else 0
     return mirror_x, angle
+
+
+def rotate_offsets_around(
+        offsets: NDArray[numpy.float64],
+        pivot: NDArray[numpy.float64],
+        angle: float,
+        ) -> NDArray[numpy.float64]:
+    """
+    Rotates offsets around a pivot point.
+    """
+    offsets -= pivot
+    offsets[:] = (rotation_matrix_2d(angle) @ offsets.T).T
+    offsets += pivot
+    return offsets
diff --git a/masque/utils/vertices.py b/masque/utils/vertices.py
index ac4a40e..826b3ec 100644
--- a/masque/utils/vertices.py
+++ b/masque/utils/vertices.py
@@ -77,7 +77,7 @@ def poly_contains_points(
     vertices = numpy.array(vertices, copy=False)
 
     if points.size == 0:
-        return numpy.zeros(0)
+        return numpy.zeros(0, dtype=numpy.int8)
 
     min_bounds = numpy.min(vertices, axis=0)[None, :]
     max_bounds = numpy.max(vertices, axis=0)[None, :]