diff --git a/pyproject.toml b/pyproject.toml
index e8f2d9d..1607409 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -54,14 +54,14 @@ sigmon = [
     "pygraphviz>=1.14",
     "typer>=0.15.1",
     "ezmsg-qt>=0.2.1",
-    "phosphor>=0.8.0",
+    "phosphor>=0.9.1",
     "pandas",
 ]
 viewer = [
     "PySide6>=6.7",
     "typer>=0.15.1",
     "ezmsg-qt>=0.2.1",
-    "phosphor>=0.8.0",
+    "phosphor>=0.9.1",
 ]
 
 [project.scripts]
diff --git a/src/ezmsg/tools/plot/__init__.py b/src/ezmsg/tools/plot/__init__.py
index 8b6ff5c..ef7143e 100644
--- a/src/ezmsg/tools/plot/__init__.py
+++ b/src/ezmsg/tools/plot/__init__.py
@@ -6,7 +6,7 @@
 :mod:`.shmem_sweep` is the Qt widget built on it, and needs the ``viewer`` or
 ``sigmon`` extra.
 
-``ShmemSweepWidget`` is resolved lazily so that importing this package, or
+``ShmemSweepWidget`` and :mod:`.layout` are resolved lazily so that importing this package, or
 anything under it, does not pull in Qt. Eagerly importing it here would make
 ``from ezmsg.tools.plot.describe import ...`` fail without phosphor installed,
 since importing a submodule runs its parent's ``__init__`` first -- which would
@@ -30,6 +30,7 @@
 )
 
 if typing.TYPE_CHECKING:  # pragma: no cover - import for type checkers only
+    from .layout import ChannelLayoutCache, channel_layout
     from .shmem_sweep import ShmemSweepWidget
 
 __all__ = [
@@ -38,7 +39,9 @@
     "MetricSpec",
     "ShmemSweepWidget",
     "StreamShape",
+    "ChannelLayoutCache",
     "UnsupportedMetricError",
+    "channel_layout",
     "describe_axisarray",
     "describe_mirror",
     "flatten_for_plot",
@@ -48,9 +51,13 @@
 
 
 def __getattr__(name: str) -> typing.Any:
-    """Resolve the Qt widget on first use (PEP 562)."""
+    """Resolve the phosphor-backed names on first use (PEP 562)."""
     if name == "ShmemSweepWidget":
         from .shmem_sweep import ShmemSweepWidget
 
         return ShmemSweepWidget
+    if name in ("channel_layout", "ChannelLayoutCache"):
+        from . import layout
+
+        return getattr(layout, name)
     raise AttributeError(f"module {__name__!r} has no attribute {name!r}")
diff --git a/src/ezmsg/tools/plot/layout.py b/src/ezmsg/tools/plot/layout.py
new file mode 100644
index 0000000..103d92b
--- /dev/null
+++ b/src/ezmsg/tools/plot/layout.py
@@ -0,0 +1,116 @@
+"""Turning a structured ``ch`` coordinate axis into a per-channel grid layout.
+
+The geometry counterpart to :mod:`ezmsg.tools.chmeta`, which does the same job
+for names. An AxisArray's ``ch`` axis may carry electrode coordinates; a grid
+plot wants positions, sizes and labels. Which fields those live in is a
+property of the acquisition system, so the decoding belongs here rather than in
+phosphor, whose grids take plain arrays and have no opinion about where they
+came from.
+
+Everything degrades: a source with no ``ch`` axis at all, or one carrying names
+but no coordinates, still gets a layout -- a square-ish tiling -- because a plot
+that draws nothing is less useful than one that draws the right number of cells
+in the wrong places.
+"""
+
+import typing
+
+import numpy as np
+
+from ..chmeta import channel_names
+
+__all__ = ["ChannelLayoutCache", "channel_layout"]
+
+DEFAULT_POSITION_FIELDS = ("x", "y")
+DEFAULT_SIZE_FIELD = "size"
+DEFAULT_GROUP_FIELD = "headstage"
+
+
+def channel_layout(
+    ch_axis_data: typing.Optional[np.ndarray],
+    n_ch: int,
+    *,
+    position_fields: typing.Tuple[str, str] = DEFAULT_POSITION_FIELDS,
+    size_field: str = DEFAULT_SIZE_FIELD,
+    group_field: typing.Optional[str] = DEFAULT_GROUP_FIELD,
+    label_fields: typing.Sequence[str] = ("label",),
+) -> typing.Tuple[np.ndarray, typing.Optional[np.ndarray], typing.List[str]]:
+    """Per-channel ``(positions, sizes, labels)`` for a grid plot.
+
+    :param ch_axis_data: The ``ch`` axis' structured data, or ``None`` when the
+        stream carries no channel metadata.
+    :param n_ch: Channels in the data, used when the axis cannot say.
+    :param position_fields: Fields holding each channel's coordinates. Both must
+        be present, or the layout falls back to a tiling.
+    :param size_field: Field holding each channel's extent. Absent gives
+        ``None``, which lets the renderer size cells by the inferred pitch.
+    :param group_field: Field identifying which device a channel belongs to.
+        Devices commonly number their electrodes from a shared origin, so
+        without this two of them draw on top of each other. ``None`` skips the
+        check.
+    :param label_fields: Passed to :func:`~ezmsg.tools.chmeta.channel_names`.
+
+    :returns: ``positions`` as ``(n, 2)`` float32, ``sizes`` as ``(n,)`` float32
+        or ``None``, and one label per channel.
+    """
+    from phosphor.grid_layout import tile_by_group, tiled_grid_positions
+
+    if ch_axis_data is None:
+        return tiled_grid_positions(n_ch), None, channel_names(None, n_ch, fields=label_fields)
+
+    fields = ch_axis_data.dtype.fields or {}
+    actual_n = ch_axis_data.shape[0]
+    x_field, y_field = position_fields
+
+    if {x_field, y_field} <= set(fields):
+        positions = np.column_stack([ch_axis_data[x_field], ch_axis_data[y_field]]).astype(np.float32)
+        if group_field and group_field in fields:
+            positions = tile_by_group(positions, ch_axis_data[group_field])
+    else:
+        positions = tiled_grid_positions(actual_n)
+
+    sizes = ch_axis_data[size_field].astype(np.float32) if size_field in fields else None
+    return positions, sizes, channel_names(ch_axis_data, actual_n, fields=label_fields)
+
+
+class ChannelLayoutCache:
+    """:func:`channel_layout`, recomputed only when the axis actually changes.
+
+    A grid that derives its layout per message pays for it per message, while
+    the answer changes about once a session. Fingerprinting the axis costs
+    around 1 us against the 75 us the derivation takes, so this is worth having
+    wherever messages arrive faster than the geometry does.
+
+    Deliberately a cache rather than a shared instance: two widgets watching one
+    stream each keep their own, so neither has to know the other exists, and the
+    derivation stays where any application can call it.
+    """
+
+    def __init__(self) -> None:
+        self._key: typing.Optional[tuple] = None
+        self._value: typing.Optional[tuple] = None
+
+    @staticmethod
+    def _fingerprint(ch_axis_data: typing.Optional[np.ndarray], n_ch: int, kwargs: dict) -> tuple:
+        """Enough to tell one layout apart from another, cheaply.
+
+        The axis' bytes rather than its identity: it arrives deserialized from
+        another process, so a new object every message describes the same
+        electrodes.
+        """
+        options = tuple(sorted((k, tuple(v) if isinstance(v, (list, tuple)) else v) for k, v in kwargs.items()))
+        if ch_axis_data is None:
+            return (n_ch, options, None)
+        return (n_ch, options, str(ch_axis_data.dtype), ch_axis_data.shape, ch_axis_data.tobytes())
+
+    def __call__(
+        self,
+        ch_axis_data: typing.Optional[np.ndarray],
+        n_ch: int,
+        **kwargs: typing.Any,
+    ) -> typing.Tuple[np.ndarray, typing.Optional[np.ndarray], typing.List[str]]:
+        key = self._fingerprint(ch_axis_data, n_ch, kwargs)
+        if key != self._key:
+            self._value = channel_layout(ch_axis_data, n_ch, **kwargs)
+            self._key = key
+        return self._value
diff --git a/tests/test_plot_layout.py b/tests/test_plot_layout.py
new file mode 100644
index 0000000..1d0ef0d
--- /dev/null
+++ b/tests/test_plot_layout.py
@@ -0,0 +1,207 @@
+"""Deriving a grid layout from a ``ch`` coordinate axis.
+
+The decoding half of the grid: which fields hold coordinates, and what to do
+when they are missing. Every fallback here exists because a plot that draws
+nothing is less useful than one that draws the right number of cells in the
+wrong places -- and because in practice the geometry is often absent, partial,
+or shared between two devices that each numbered from their own origin.
+"""
+
+import numpy as np
+import pytest
+
+# The geometry helpers this builds on live in phosphor, which is an optional
+# extra -- so a runner that installs only the test group cannot reach them.
+# Same guard as test_shmem_sweep, and skipped for the same reason.
+# Keyed on phosphor itself, not on the module under test: layout.py imports it
+# inside the function, so the module imports fine without it and only fails when
+# called.
+pytest.importorskip(
+    "phosphor.grid_layout",
+    reason="needs phosphor (the 'viewer' or 'sigmon' extra)",
+    exc_type=ImportError,
+)
+
+from ezmsg.tools.plot import ChannelLayoutCache, channel_layout  # noqa: E402
+
+GEOMETRY = np.dtype([("x", "f4"), ("y", "f4"), ("size", "f4"), ("label", "U8"), ("headstage", "i4")])
+
+
+def make_axis(n=4, *, fields=("x", "y", "size", "label", "headstage")):
+    """A ``ch`` axis carrying only the named fields."""
+    dt = np.dtype([(name, GEOMETRY[name]) for name in fields])
+    ch = np.zeros(n, dtype=dt)
+    if "x" in fields:
+        ch["x"] = np.arange(n) % 2
+    if "y" in fields:
+        ch["y"] = np.arange(n) // 2
+    if "size" in fields:
+        ch["size"] = 0.5
+    if "label" in fields:
+        ch["label"] = [f"E{i}" for i in range(n)]
+    return ch
+
+
+def test_coordinates_are_used_verbatim():
+    ch = make_axis(4, fields=("x", "y"))
+    positions, sizes, labels = channel_layout(ch, 4)
+
+    np.testing.assert_allclose(positions, [[0, 0], [1, 0], [0, 1], [1, 1]])
+    assert sizes is None, "no size field means the renderer picks from the pitch"
+    assert labels == ["ch0", "ch1", "ch2", "ch3"]
+
+
+def test_sizes_and_labels_come_along_when_present():
+    positions, sizes, labels = channel_layout(make_axis(4), 4)
+    assert positions.shape == (4, 2)
+    np.testing.assert_allclose(sizes, 0.5)
+    assert labels == ["E0", "E1", "E2", "E3"]
+
+
+def test_devices_sharing_a_coordinate_range_are_separated():
+    """Two headstages numbering electrodes from the same origin would otherwise
+    render one on top of the other."""
+    ch = make_axis(4)
+    ch["x"] = [0, 1, 0, 1]
+    ch["y"] = [0, 0, 0, 0]
+    ch["headstage"] = [0, 0, 1, 1]
+
+    positions, _, _ = channel_layout(ch, 4)
+    assert positions[2, 0] > positions[1, 0], "the second device must start clear of the first"
+
+
+def test_the_grouping_field_can_be_ignored():
+    ch = make_axis(4)
+    ch["x"] = [0, 1, 0, 1]
+    ch["headstage"] = [0, 0, 1, 1]
+
+    positions, _, _ = channel_layout(ch, 4, group_field=None)
+    np.testing.assert_allclose(positions[:, 0], [0, 1, 0, 1])
+
+
+def test_an_axis_without_coordinates_still_gets_a_layout():
+    """Channel names but no geometry: common for LSL and plain NWB streams."""
+    ch = make_axis(4, fields=("label",))
+    positions, sizes, labels = channel_layout(ch, 4)
+
+    assert positions.shape == (4, 2)
+    assert len({tuple(p) for p in positions}) == 4, "cells must not stack"
+    assert sizes is None
+    assert labels == ["E0", "E1", "E2", "E3"], "names survive even with no geometry"
+
+
+def test_no_channel_axis_at_all_still_gets_a_layout():
+    positions, sizes, labels = channel_layout(None, 3)
+    assert positions.shape == (3, 2)
+    assert sizes is None
+    assert labels == ["ch0", "ch1", "ch2"]
+
+
+def test_only_one_coordinate_is_not_half_a_layout():
+    """An x with no y cannot place anything; falling back is the honest move."""
+    ch = make_axis(4, fields=("x", "label"))
+    positions, _, _ = channel_layout(ch, 4)
+    assert len({tuple(p) for p in positions}) == 4
+
+
+def test_the_coordinate_fields_are_configurable():
+    """Nothing says a source must call them x and y."""
+    dt = np.dtype([("col", "f4"), ("row", "f4")])
+    ch = np.zeros(3, dtype=dt)
+    ch["col"] = [5.0, 6.0, 7.0]
+    ch["row"] = 1.0
+
+    positions, _, _ = channel_layout(ch, 3, position_fields=("col", "row"))
+    np.testing.assert_allclose(positions[:, 0], [5.0, 6.0, 7.0])
+
+
+def test_labels_follow_the_requested_fields():
+    """The same choice the sweep offers: a Blackrock user reads bank and elec
+    off the front panel, not a label field."""
+    dt = np.dtype([("x", "f4"), ("y", "f4"), ("bank", "U4"), ("elec", "i4")])
+    ch = np.zeros(2, dtype=dt)
+    ch["bank"] = ["A", "A"]
+    ch["elec"] = [1, 2]
+
+    _, _, labels = channel_layout(ch, 2, label_fields=("bank", "elec"))
+    assert labels == ["A-1", "A-2"]
+
+
+def test_the_axis_decides_the_count_when_it_disagrees():
+    """The axis is the thing that knows how many rows it has; trusting a stale
+    n_ch would index off the end of it."""
+    ch = make_axis(4)
+    positions, sizes, labels = channel_layout(ch, 99)
+    assert positions.shape[0] == 4
+    assert len(labels) == 4
+
+
+@pytest.mark.parametrize("n", [0, 1])
+def test_degenerate_channel_counts_do_not_raise(n):
+    positions, _, labels = channel_layout(None, n)
+    assert positions.shape == (n, 2)
+    assert len(labels) == n
+
+
+# ---- caching ----------------------------------------------------------------
+#
+# A grid deriving its layout per message pays per message, while the answer
+# changes about once a session.
+
+
+def test_an_unchanged_axis_is_not_derived_twice():
+    cache = ChannelLayoutCache()
+    ch = make_axis(4)
+    assert cache(ch, 4) is cache(ch, 4)
+
+
+def test_an_equal_but_distinct_axis_still_hits():
+    """The axis arrives deserialized from another process, so it is a new object
+    every message while describing the same electrodes. Keying on identity would
+    make the cache useless exactly where it is needed."""
+    cache = ChannelLayoutCache()
+    ch = make_axis(4)
+    first = cache(ch, 4)
+    assert cache(ch.copy(), 4) is first
+
+
+def test_a_changed_axis_is_derived_again():
+    cache = ChannelLayoutCache()
+    ch = make_axis(4)
+    first = cache(ch, 4)
+
+    moved = ch.copy()
+    moved["x"][0] = 99.0
+    second = cache(moved, 4)
+
+    assert second is not first
+    assert second[0][0, 0] == pytest.approx(99.0)
+
+
+def test_a_changed_channel_count_is_derived_again():
+    cache = ChannelLayoutCache()
+    assert cache(None, 4) is not cache(None, 9)
+
+
+def test_changed_options_are_derived_again():
+    """Same axis, different question -- the answer is not the cached one."""
+    dt = np.dtype([("x", "f4"), ("y", "f4"), ("bank", "U4"), ("elec", "i4")])
+    ch = np.zeros(2, dtype=dt)
+    ch["bank"] = ["A", "A"]
+    ch["elec"] = [1, 2]
+
+    cache = ChannelLayoutCache()
+    assert cache(ch, 2)[2] == ["ch0", "ch1"]
+    assert cache(ch, 2, label_fields=("bank", "elec"))[2] == ["A-1", "A-2"]
+
+
+def test_no_axis_at_all_caches_too():
+    cache = ChannelLayoutCache()
+    assert cache(None, 3) is cache(None, 3)
+
+
+def test_two_caches_do_not_share():
+    """Each consumer keeps its own, so neither has to know the other exists."""
+    a, b = ChannelLayoutCache(), ChannelLayoutCache()
+    ch = make_axis(4)
+    assert a(ch, 4) is not b(ch, 4)