diff --git a/packages/ludic.nav/index.ludic b/packages/ludic.nav/index.ludic
index 8ad555c6..d4b4936a 100644
--- a/packages/ludic.nav/index.ludic
+++ b/packages/ludic.nav/index.ludic
@@ -10,3 +10,4 @@ import "build.ludic"
 import "query.ludic"
 import "crowd.ludic"
 import "resident.ludic"
+import "resident_count.ludic"
diff --git a/packages/ludic.nav/resident.ludic b/packages/ludic.nav/resident.ludic
index 43683a9a..1c74ae6a 100644
--- a/packages/ludic.nav/resident.ludic
+++ b/packages/ludic.nav/resident.ludic
@@ -51,6 +51,23 @@ export function nav_tiles_keep(nav_st: NavState, kind: int, xs: []float, zs: []f
   }
   return changed
 }
+# the same ring by a distance the game answers: near(x, z) is how far (x, z) is from what must be
+# loaded (0 inside it). A tile comes in when its centre is within pad of that, and goes only past
+# pad + hyst, so a player at an edge does not read one in and out; how many changed
+export function nav_tiles_keep_near(nav_st: NavState, kind: int, near: fn(float, float) -> float, pad: float, hyst: float) -> int {
+  let h = nv_mesh(nav_st, kind)
+  let f = nav_st.nv_files[kind]
+  if h == null or f == null { return 0 }
+  var changed = 0
+  for i in 0 .. nvc_index_count(h) {
+    nvc_index_tile(h, i, nav_st.nv_tile)
+    let m = near(nav_st.nv_tile[0], nav_st.nv_tile[1]) - pad
+    let is_in = nav_st.nv_tile[2] > 0.5
+    if is_in and m > hyst { changed += nvc_index_out(h, i) }
+    if not is_in and m < 0.0 { changed += nv_tile_read(h, f, i) }
+  }
+  return changed
+}
 function nv_tile_read(h: pointer, f: pointer, i: int) -> int {
   let size = nvc_index_size(h, i)
   let buf = nvc_stage(size)
@@ -62,24 +79,3 @@ function nv_tile_read(h: pointer, f: pointer, i: int) -> int {
   }
   return nvc_index_in(h, i, buf, size)
 }
-
-# how many of kind's tiles are in, and (nav_tiles_bytes) how many bytes those hold
-export function nav_tiles_in(nav_st: NavState, kind: int) -> int { return nv_tiles_sum(nav_st, kind, false) }
-export function nav_tiles_bytes(nav_st: NavState, kind: int) -> int { return nv_tiles_sum(nav_st, kind, true) }
-function nv_tiles_sum(nav_st: NavState, kind: int, bytes: bool) -> int {
-  let h = nv_mesh(nav_st, kind)
-  if h == null { return 0 }
-  var n = 0
-  for i in 0 .. nvc_index_count(h) {
-    nvc_index_tile(h, i, nav_st.nv_tile)
-    if nav_st.nv_tile[2] > 0.5 and bytes { n += int(nav_st.nv_tile[3]) }
-    if nav_st.nv_tile[2] > 0.5 and not bytes { n += 1 }
-  }
-  return n
-}
-# how many tiles kind's file holds in all
-export function nav_tiles_all(nav_st: NavState, kind: int) -> int {
-  let h = nv_mesh(nav_st, kind)
-  if h == null { return 0 }
-  return nvc_index_count(h)
-}
diff --git a/packages/ludic.nav/resident_count.ludic b/packages/ludic.nav/resident_count.ludic
new file mode 100644
index 00000000..a38ed00a
--- /dev/null
+++ b/packages/ludic.nav/resident_count.ludic
@@ -0,0 +1,21 @@
+# resident_count.ludic - what a file-backed mesh holds now: its tiles in, their bytes, and how many it has
+# how many of kind's tiles are in, and (nav_tiles_bytes) how many bytes those hold
+export function nav_tiles_in(nav_st: NavState, kind: int) -> int { return nv_tiles_sum(nav_st, kind, false) }
+export function nav_tiles_bytes(nav_st: NavState, kind: int) -> int { return nv_tiles_sum(nav_st, kind, true) }
+function nv_tiles_sum(nav_st: NavState, kind: int, bytes: bool) -> int {
+  let h = nv_mesh(nav_st, kind)
+  if h == null { return 0 }
+  var n = 0
+  for i in 0 .. nvc_index_count(h) {
+    nvc_index_tile(h, i, nav_st.nv_tile)
+    if nav_st.nv_tile[2] > 0.5 and bytes { n += int(nav_st.nv_tile[3]) }
+    if nav_st.nv_tile[2] > 0.5 and not bytes { n += 1 }
+  }
+  return n
+}
+# how many tiles kind's file holds in all
+export function nav_tiles_all(nav_st: NavState, kind: int) -> int {
+  let h = nv_mesh(nav_st, kind)
+  if h == null { return 0 }
+  return nvc_index_count(h)
+}
diff --git a/packages/ludic.nav/tests/keep_near_test.ludic b/packages/ludic.nav/tests/keep_near_test.ludic
new file mode 100644
index 00000000..2ab699f6
--- /dev/null
+++ b/packages/ludic.nav/tests/keep_near_test.ludic
@@ -0,0 +1,47 @@
+# keep_near_test.ludic - a file-backed mesh's tiles kept by a distance the game answers (its players'
+# zones): a zone round one corner brings in its tile only, growing it brings in its neighbours, an
+# edge nudged back and forth changes nothing, and a zone moved far away lets them all go
+import "ludic.nav"
+import "ludic.base"
+import "fakes/meadow.ludic"
+program KeepNearTest {
+  numbers float
+
+  state NearState {
+    x: float = 0.0
+    z: float = 0.0
+    r: float = 0.0
+  }
+  # metres from (x, z) to the zone's edge, 0 inside: what ludic.zones' zones_nearest answers
+  function near(near_st: NearState, x: float, z: float) -> float {
+    let d = Math.sqrt((x - near_st.x) * (x - near_st.x) + (z - near_st.z) * (z - near_st.z))
+    return Math.max(d - near_st.r, 0.0)
+  }
+  function in_zone(nav_st: NavState) -> int { return nav_tiles_keep_near(nav_st, NAV_PERSON, fn near, 46.0, 200.0) }
+
+  test "tiles come in within the zone, an edge nudged back and forth changes nothing, and a far zone lets them go" (nav_st: mut NavState, near_st: mut NearState) {
+    let g = ground(128, 0)
+    expect(nav_tiled(nav_st, NAV_PERSON, 0.0, 0.0, 64.0, 16, 4096))
+    for tz in 0 .. 2 { for tx in 0 .. 2 { expect(nav_tile_build(nav_st, NAV_PERSON, tx, tz, g, new NavConfig) > 0) } }
+    let path = Os.temp_dir() + "/ludic_nav_near.navmesh"
+    expect(nav_save_file(nav_st, NAV_PERSON, path))
+    nav_reset(nav_st)
+    expect(nav_load_index(nav_st, NAV_PERSON, path))
+    near_st.x = 10.0
+    near_st.z = 10.0
+    near_st.r = 5.0
+    expect_eq(in_zone(nav_st), 1)
+    expect_eq(nav_tiles_in(nav_st, NAV_PERSON), 1)
+    near_st.r = 80.0
+    expect_eq(in_zone(nav_st), 3)
+    expect_eq(nav_tiles_in(nav_st, NAV_PERSON), 4)
+    for k in 0 .. 20 {
+      near_st.r = 5.0 + float(k % 2) * 100.0
+      expect_eq(in_zone(nav_st), 0)
+    }
+    near_st.x = 2000.0
+    expect_eq(in_zone(nav_st), 4)
+    expect_eq(nav_tiles_in(nav_st, NAV_PERSON), 0)
+    nav_reset(nav_st)
+  }
+}