diff --git a/changes/zones.md b/changes/zones.md
new file mode 100644
index 00000000..558be25a
--- /dev/null
+++ b/changes/zones.md
@@ -0,0 +1,10 @@
+bump: minor
+type: feature
+**`ludic.zones`: where a world is simulated.** A disc per player, `(x, z, r)` with `r = zones_radius(fog)`
+(the fog distance plus 40 m, never under 150 m, 900 m with no fog), overlapping discs merged into
+clusters with a bounding circle, and `zones_contains` / `zones_nearest` for everything that asks; fixed
+arrays, nothing made per frame. The packages that simulate now ask their world port whether a place is
+simulated, with a default of everywhere: `WildlifeWorld.active` (an animal outside is frozen - its
+state kept, no dice drawn), `NpcWorld.active` (a walker outside is frozen, and nobody is born outside),
+`VehicleWorld.active` (a moored boat outside is left where it lies) and `ThingsWorld.restocks` (a
+morning restocks only inside).
diff --git a/packages/README.md b/packages/README.md
index 62f7ecef..5bbcd517 100644
--- a/packages/README.md
+++ b/packages/README.md
@@ -22,6 +22,7 @@ section. The rules are in [ludic.base](ludic.base/README.md).
 | [ludic.crafting](ludic.crafting/README.md) | recipes: what goes in and out, where and how long, making, refunding, hold-to-make |
 | [ludic.effects](ludic.effects/README.md) | timed modifiers that run down in game time (a meal's warmth, a drink's legs) |
 | [ludic.fire](ludic.fire/README.md) | a camp fire: fuel, the rain on it, warmth at a distance, whether it will cook |
+| [ludic.zones](ludic.zones/README.md) | where the world is simulated: a disc per player from their fog, merged into clusters |
 | [ludic.fishing](ludic.fishing/README.md) | a rod at the water: cast, bite, the reel's fight, the landing; species as an open registry |
 | [ludic.hints](ludic.hints/README.md) | a rail of what is true now, most urgent first, each a card that teaches it and can be muted by key |
 | [ludic.i18n](ludic.i18n/README.md) | a game in any language: gettext `.po` files, patterns with holes, plurals, a mod folder, a font per language |
diff --git a/packages/ludic.npc/census.ludic b/packages/ludic.npc/census.ludic
index fabcb699..f1890c3e 100644
--- a/packages/ludic.npc/census.ludic
+++ b/packages/ludic.npc/census.ludic
@@ -27,6 +27,7 @@ export function npc_spawn(npc_st: mut NpcState, kind: int) -> NpcPerson {
     let start = k.start
     start(p)
   } else { npc_start_near(npc_st, p, NpcWorld.origin_x(), NpcWorld.origin_z(), 6.0, 30.0) }
+  if not NpcWorld.active(p.x, p.z) { return null }   # nobody is born outside every zone; the slot waits
   p.active = true
   npc_st.np_n += 1
   NpcWorld.born(p)
diff --git a/packages/ludic.npc/port.ludic b/packages/ludic.npc/port.ludic
index 908588a4..69aa96e8 100644
--- a/packages/ludic.npc/port.ludic
+++ b/packages/ludic.npc/port.ludic
@@ -5,6 +5,7 @@ export port NpcWorld {
   water: fn(float, float) -> float = fn nw_dry             # the water's surface there
   slope: fn(float, float) -> float = fn nw_zero2
   allowed: fn(float, float) -> bool = fn nw_yes2           # a person may stop here (not the player's camp)
+  active: fn(float, float) -> bool = fn nw_yes2            # simulated here: outside, a walker is frozen and none is born
   # (x, z, r, feet, head): true when a still thing takes a body of radius r there; pushed_x / _z say where
   push: fn(float, float, float, float, float) -> bool = fn nw_no_push
   pushed_x: fn() -> float = fn nw_asked_x
diff --git a/packages/ludic.npc/tick.ludic b/packages/ludic.npc/tick.ludic
index ae7c8a48..34a2dae3 100644
--- a/packages/ludic.npc/tick.ludic
+++ b/packages/ludic.npc/tick.ludic
@@ -6,7 +6,7 @@ export function npc_tick(npc_st: mut NpcState, dt: float) -> void {
   np_census(npc_st)
   for i in 0 .. len(npc_st.np_walkers) {
     let p = npc_st.np_walkers[i]
-    if not p.active or np_leaves(npc_st, p) { continue }
+    if not p.active or not NpcWorld.active(p.x, p.z) or np_leaves(npc_st, p) { continue }
     p.goal_speed = 0.0
     if p.act == NPCA_WALK { npc_walk(npc_st, p, dt) } else { npc_act(npc_st, p, dt) }
     npc_notice(npc_st, p)
diff --git a/packages/ludic.things/dispatch.ludic b/packages/ludic.things/dispatch.ludic
index 737bb017..7b18648e 100644
--- a/packages/ludic.things/dispatch.ludic
+++ b/packages/ludic.things/dispatch.ludic
@@ -70,7 +70,7 @@ export function things_restock(things_st: ThingsState) -> void {
   let all = things_all(things_st)
   for i in 0 .. len(all) {
     let t = all[i]
-    if thing_is_put_down(t) { continue }
+    if thing_is_put_down(t) or not ThingsWorld.restocks(t.x, t.z) { continue }
     if not ThingKinds[t.kind].keeps { t.used = 0 }
     if not t.active { thing_show(t) }
   }
diff --git a/packages/ludic.things/port.ludic b/packages/ludic.things/port.ludic
index 8070e0b6..00a633a8 100644
--- a/packages/ludic.things/port.ludic
+++ b/packages/ludic.things/port.ludic
@@ -5,6 +5,7 @@ export port ThingsWorld {
   placed: fn(Thing) -> void = fn th_nothing           # a Thing exists now: draw it
   removed: fn(Thing) -> void = fn th_nothing          # it is gone for good: stop drawing it
   shown: fn(Thing) -> void = fn th_nothing            # its `active` changed: show or hide it
+  restocks: fn(float, float) -> bool = fn th_yes2      # a morning restocks here (inside a zone)
   moved: fn(Thing) -> void = fn th_nothing            # it stands somewhere else now
   keeps: fn(Thing) -> bool = fn th_kind_saves         # the save's section carries it
   put_down: fn(Thing) -> bool = fn th_kind_put_down   # set down by someone: a restock leaves it be
@@ -12,5 +13,6 @@ export port ThingsWorld {
 }
 function th_flat(x: float, z: float) -> float { return 0.0 }
 function th_nothing(t: Thing) -> void { }
+function th_yes2(x: float, z: float) -> bool { return true }
 function th_kind_saves(t: Thing) -> bool { return thing_kind_ok(t.kind) and ThingKinds[t.kind].saved }
 function th_kind_put_down(t: Thing) -> bool { return thing_kind_ok(t.kind) and ThingKinds[t.kind].put_down }
diff --git a/packages/ludic.vehicles/ports.ludic b/packages/ludic.vehicles/ports.ludic
index a6c10395..b60f5419 100644
--- a/packages/ludic.vehicles/ports.ludic
+++ b/packages/ludic.vehicles/ports.ludic
@@ -11,6 +11,7 @@ export port VehicleWorld {
   made: fn(Vehicle) -> void = fn ve__nothing               # a new vehicle: draw it
   placed: fn(Vehicle) -> void = fn ve__nothing             # it moved: put its model there
   gone: fn(Vehicle) -> void = fn ve__nothing               # its owner left: take it away
+  active: fn(float, float) -> bool = fn ve__yes2           # simulated here: outside, a moored boat is left as it is
 }
 
 # a boat's hull in the world's physics (Maroon Lake: a buoyant Jolt body), named by the vehicle's
@@ -70,6 +71,7 @@ export state VehiclesState {
 function ve__dry(x: float, z: float) -> float { return -10000.0 }
 function ve__calm(x: float, z: float, fx: float, fz: float) -> float { return 0.0 }
 function ve__zero() -> float { return 0.0 }
+function ve__yes2(x: float, z: float) -> bool { return true }
 function ve__next(vehicles_st: mut VehiclesState) -> int {
   vehicles_st.ve_ids += 1
   return vehicles_st.ve_ids
diff --git a/packages/ludic.vehicles/ride.ludic b/packages/ludic.vehicles/ride.ludic
index 53eb95f5..3ea53bcd 100644
--- a/packages/ludic.vehicles/ride.ludic
+++ b/packages/ludic.vehicles/ride.ludic
@@ -64,6 +64,7 @@ export function vehicles_tick(vehicles_st: VehiclesState, dt: float) -> void {
       if w > 0.0 { VehicleHull.drift(v.nid, -Math.sin(wy) * w, -Math.cos(wy) * w) }
       continue
     }
+    if not VehicleWorld.active(v.x, v.z) { continue }   # outside every zone: left where it lies
     ve_hull_read(v)
     ve_hold(v)
     VehicleWorld.placed(v)
diff --git a/packages/ludic.wildlife/port.ludic b/packages/ludic.wildlife/port.ludic
index 7c599b5c..34bd1198 100644
--- a/packages/ludic.wildlife/port.ludic
+++ b/packages/ludic.wildlife/port.ludic
@@ -38,6 +38,7 @@ export port WildlifeWorld {
   taught: fn() -> bool = fn wl_no0                        # food carries further, feeders mind less
   about: fn(WildAnimal) -> int = fn wl_about              # WILD_ABOUT, _AWAY or _GONE
   ranges: fn(int) -> int = fn wl_two                      # ranges a species gets on this map
+  active: fn(float, float) -> bool = fn wl_yes2           # simulated here: outside, an animal is frozen
   per_range: fn(int) -> int = fn wl_three                 # and how many live in each
   spot: fn(WildAnimal, bool, WildSpot) -> bool = fn wl_no_spot   # water (true) or forage for it
   lures: fn() -> int = fn wl_none0                        # how many things to ask `lure` about
@@ -62,6 +63,7 @@ function wl_no0() -> bool { return false }
 function wl_no1(p: int) -> bool { return false }
 function wl_no2(x: float, z: float) -> bool { return false }
 function wl_yes1(u: int) -> bool { return true }
+function wl_yes2(x: float, z: float) -> bool { return true }
 function wl_clear(ax: float, ay: float, az: float, bx: float, by: float, bz: float) -> bool { return true }
 function wl_no_push(x: float, z: float, r: float, y0: float, y1: float) -> bool { return false }
 function wl_asked_x(wildlife_st: WildlifeState) -> float { return wildlife_st.wl_ask_x }
diff --git a/packages/ludic.wildlife/run.ludic b/packages/ludic.wildlife/run.ludic
index 248333e5..437fd61b 100644
--- a/packages/ludic.wildlife/run.ludic
+++ b/packages/ludic.wildlife/run.ludic
@@ -1,5 +1,5 @@
-# run.ludic - one step of every animal: the port says whether it is about at this hour; anything
-# within 900 m of a player thinks; the gait follows the ground covered; player 0 sees what is near
+# run.ludic - one step of every animal inside a zone (WildlifeWorld.active): the port says whether it
+# is about at this hour; within 900 m of a player it thinks; player 0 sees what is near
 export function wildlife_tick(wildlife_st: mut WildlifeState, dt: float, gh: float) -> void {
   wl_seed_scan(wildlife_st, dt)
   let all = wildlife_all(wildlife_st)
@@ -9,6 +9,7 @@ export function wildlife_tick(wildlife_st: mut WildlifeState, dt: float, gh: flo
 
 function wl_tick_one(wildlife_st: mut WildlifeState, a: WildAnimal, dt: float, gh: float) -> void {
   if not a.alive { return }
+  if not WildlifeWorld.active(a.x, a.z) { return }   # outside every zone: its state kept, no dice drawn
   let about = WildlifeWorld.about(a)
   if about == WILD_AWAY {
     a.shown = false
diff --git a/packages/ludic.zones/README.md b/packages/ludic.zones/README.md
new file mode 100644
index 00000000..979d7f82
--- /dev/null
+++ b/packages/ludic.zones/README.md
@@ -0,0 +1,16 @@
+# ludic.zones
+
+Where a world is simulated: a disc per player - `(x, z, r)`, `r = zones_radius(fog)`, that is the
+fog distance plus 40 m and never under 150 m, 900 m with no fog - and the discs that overlap merged
+into clusters with a bounding circle. Uses `ludic.base` and nothing else.
+
+- `zones_set(pid, x, z, r)`, `zones_clear(pid)`, `zones_reset()`; `zones_merge()` once a frame
+  after the discs are set, for the clusters.
+- `zones_contains(x, z)`: inside any disc. `zones_nearest(x, z)`: metres to the nearest disc's
+  edge, 0 inside. With no disc set, everywhere is inside (0) - a world before its first frame
+  freezes nothing.
+- `zones_clusters()`, `zones_cluster_x / _z / _r / _n(c)`, `zones_cluster_of(pid)`.
+
+The rules it keeps: fixed arrays of `ZONES_MAX` (16) slots, nothing made after the state; the
+questions allocate nothing. A world gates its ticks on `zones_contains` so what is outside every
+zone keeps its state and draws no dice.
diff --git a/packages/ludic.zones/ask.ludic b/packages/ludic.zones/ask.ludic
new file mode 100644
index 00000000..cefe5ba7
--- /dev/null
+++ b/packages/ludic.zones/ask.ludic
@@ -0,0 +1,41 @@
+# ask.ludic - the questions: inside any disc, how far outside the nearest, and the clusters. With no
+# disc set yet (a world before its first frame) everywhere is inside, so nothing freezes by accident
+export function zones_any(zones_st: ZonesState) -> bool {
+  for i in 0 .. ZONES_MAX { if zones_st.zn_on[i] != 0 { return true } }
+  return false
+}
+
+export function zones_contains(zones_st: ZonesState, x: float, z: float) -> bool {
+  var any = false
+  for i in 0 .. ZONES_MAX {
+    if zones_st.zn_on[i] == 0 { continue }
+    any = true
+    let dx = x - zones_st.zn_x[i]
+    let dz = z - zones_st.zn_z[i]
+    if dx * dx + dz * dz <= zones_st.zn_r[i] * zones_st.zn_r[i] { return true }
+  }
+  return not any
+}
+
+# metres from (x, z) to the edge of the nearest disc: 0 inside one (and 0 with no disc set)
+export function zones_nearest(zones_st: ZonesState, x: float, z: float) -> float {
+  var best = -1.0
+  for i in 0 .. ZONES_MAX {
+    if zones_st.zn_on[i] == 0 { continue }
+    let dx = x - zones_st.zn_x[i]
+    let dz = z - zones_st.zn_z[i]
+    let d = Math.max(Math.sqrt(dx * dx + dz * dz) - zones_st.zn_r[i], 0.0)
+    if best < 0.0 or d < best { best = d }
+  }
+  if best < 0.0 { return 0.0 }
+  return best
+}
+
+export function zones_on(zones_st: ZonesState, pid: int) -> bool { return pid >= 0 and pid < ZONES_MAX and zones_st.zn_on[pid] != 0 }
+export function zones_r(zones_st: ZonesState, pid: int) -> float { return zones_st.zn_r[pid] }
+export function zones_cluster_of(zones_st: ZonesState, pid: int) -> int { return zones_st.zn_cl[pid] }
+export function zones_clusters(zones_st: ZonesState) -> int { return zones_st.zn_ncl }
+export function zones_cluster_x(zones_st: ZonesState, c: int) -> float { return zones_st.zn_cx[c] }
+export function zones_cluster_z(zones_st: ZonesState, c: int) -> float { return zones_st.zn_cz[c] }
+export function zones_cluster_r(zones_st: ZonesState, c: int) -> float { return zones_st.zn_cr[c] }
+export function zones_cluster_n(zones_st: ZonesState, c: int) -> int { return zones_st.zn_cn[c] }
diff --git a/packages/ludic.zones/index.ludic b/packages/ludic.zones/index.ludic
new file mode 100644
index 00000000..82819c01
--- /dev/null
+++ b/packages/ludic.zones/index.ludic
@@ -0,0 +1,8 @@
+# ludic.zones - a disc per player (x, z, r), the discs that overlap merged into clusters with a
+# bounding circle, and the questions a world asks of them; fixed arrays, nothing made per frame
+module ludic_zones uses ludic_base
+numbers float
+import "ludic.base"
+import "state.ludic"
+import "merge.ludic"
+import "ask.ludic"
diff --git a/packages/ludic.zones/merge.ludic b/packages/ludic.zones/merge.ludic
new file mode 100644
index 00000000..884f596c
--- /dev/null
+++ b/packages/ludic.zones/merge.ludic
@@ -0,0 +1,70 @@
+# merge.ludic - discs that overlap (or touch) are one cluster, transitively; a cluster's bounding
+# circle is centred on its discs' box and reaches the farthest edge
+export function zones_merge(zones_st: mut ZonesState) -> void {
+  for i in 0 .. ZONES_MAX { zones_st.zn_up[i] = i }
+  for i in 0 .. ZONES_MAX {
+    if zones_st.zn_on[i] == 0 { continue }
+    for j in i + 1 .. ZONES_MAX { if zones_st.zn_on[j] != 0 and zn_touch(zones_st, i, j) { zn_join(zones_st, i, j) } }
+  }
+  zones_st.zn_ncl = 0
+  for i in 0 .. ZONES_MAX { zones_st.zn_cl[i] = -1 }
+  for i in 0 .. ZONES_MAX {
+    if zones_st.zn_on[i] == 0 { continue }
+    let root = zn_root(zones_st, i)
+    if zones_st.zn_cl[root] < 0 {
+      zones_st.zn_cl[root] = zones_st.zn_ncl
+      zones_st.zn_ncl += 1
+    }
+    zones_st.zn_cl[i] = zones_st.zn_cl[root]
+  }
+  for c in 0 .. zones_st.zn_ncl { zn_bound(zones_st, c) }
+}
+
+function zn_touch(zones_st: ZonesState, i: int, j: int) -> bool {
+  let dx = zones_st.zn_x[i] - zones_st.zn_x[j]
+  let dz = zones_st.zn_z[i] - zones_st.zn_z[j]
+  let rr = zones_st.zn_r[i] + zones_st.zn_r[j]
+  return dx * dx + dz * dz <= rr * rr
+}
+
+function zn_root(zones_st: ZonesState, i: int) -> int {
+  var k = i
+  while zones_st.zn_up[k] != k { k = zones_st.zn_up[k] }
+  return k
+}
+
+function zn_join(zones_st: mut ZonesState, i: int, j: int) -> void {
+  let a = zn_root(zones_st, i)
+  let b = zn_root(zones_st, j)
+  if a < b { zones_st.zn_up[b] = a }
+  if b < a { zones_st.zn_up[a] = b }
+}
+
+function zn_bound(zones_st: mut ZonesState, c: int) -> void {
+  var x0 = 1000000000.0
+  var x1 = -1000000000.0
+  var z0 = 1000000000.0
+  var z1 = -1000000000.0
+  var n = 0
+  for i in 0 .. ZONES_MAX {
+    if zones_st.zn_on[i] == 0 or zones_st.zn_cl[i] != c { continue }
+    x0 = Math.min(x0, zones_st.zn_x[i] - zones_st.zn_r[i])
+    x1 = Math.max(x1, zones_st.zn_x[i] + zones_st.zn_r[i])
+    z0 = Math.min(z0, zones_st.zn_z[i] - zones_st.zn_r[i])
+    z1 = Math.max(z1, zones_st.zn_z[i] + zones_st.zn_r[i])
+    n += 1
+  }
+  let cx = (x0 + x1) * 0.5
+  let cz = (z0 + z1) * 0.5
+  var r = 0.0
+  for i in 0 .. ZONES_MAX {
+    if zones_st.zn_on[i] == 0 or zones_st.zn_cl[i] != c { continue }
+    let dx = zones_st.zn_x[i] - cx
+    let dz = zones_st.zn_z[i] - cz
+    r = Math.max(r, Math.sqrt(dx * dx + dz * dz) + zones_st.zn_r[i])
+  }
+  zones_st.zn_cx[c] = cx
+  zones_st.zn_cz[c] = cz
+  zones_st.zn_cr[c] = r
+  zones_st.zn_cn[c] = n
+}
diff --git a/packages/ludic.zones/package.ludic b/packages/ludic.zones/package.ludic
new file mode 100644
index 00000000..1e094e5d
--- /dev/null
+++ b/packages/ludic.zones/package.ludic
@@ -0,0 +1,5 @@
+# ludic.zones - where the world is simulated: a disc per player, overlapping discs merged into
+# clusters, asked whether a point is inside any. Uses ludic.base and nothing else.
+package "ludic.zones"
+version "0.1.0"
+kind source
diff --git a/packages/ludic.zones/state.ludic b/packages/ludic.zones/state.ludic
new file mode 100644
index 00000000..48a76c6e
--- /dev/null
+++ b/packages/ludic.zones/state.ludic
@@ -0,0 +1,40 @@
+# state.ludic - the discs by player slot and the clusters the last merge made
+export const ZONES_MAX: int = 16             # player slots a world can hold (at least PLY_MAX)
+export const ZONES_NO_FOG: float = 900.0     # the radius of a player who sees to the horizon
+export const ZONES_PAST_FOG: float = 40.0    # simulated this far past what a player can see
+export const ZONES_LEAST: float = 150.0      # and never less than this
+
+export state ZonesState {
+  zn_on: words = words(ZONES_MAX)
+  zn_x: []float = floats(ZONES_MAX)
+  zn_z: []float = floats(ZONES_MAX)
+  zn_r: []float = floats(ZONES_MAX)
+  zn_cl: words = words(ZONES_MAX)             # each disc's cluster, after zones_merge
+  zn_up: words = words(ZONES_MAX)             # the merge's union-find
+  zn_ncl: int = 0
+  zn_cx: []float = floats(ZONES_MAX)         # each cluster's bounding circle
+  zn_cz: []float = floats(ZONES_MAX)
+  zn_cr: []float = floats(ZONES_MAX)
+  zn_cn: words = words(ZONES_MAX)             # how many discs it holds
+}
+
+# a player's radius from how far they see: fog_dist <= 0 is no fog
+export function zones_radius(fog_dist: float) -> float {
+  if fog_dist <= 0.0 { return ZONES_NO_FOG }
+  return Math.max(fog_dist + ZONES_PAST_FOG, ZONES_LEAST)
+}
+
+export function zones_set(zones_st: mut ZonesState, pid: int, x: float, z: float, r: float) -> void {
+  if pid < 0 or pid >= ZONES_MAX { return }
+  zones_st.zn_on[pid] = 1
+  zones_st.zn_x[pid] = x
+  zones_st.zn_z[pid] = z
+  zones_st.zn_r[pid] = r
+}
+
+export function zones_clear(zones_st: mut ZonesState, pid: int) -> void { if pid >= 0 and pid < ZONES_MAX { zones_st.zn_on[pid] = 0 } }
+
+export function zones_reset(zones_st: mut ZonesState) -> void {
+  for i in 0 .. ZONES_MAX { zones_st.zn_on[i] = 0 }
+  zones_st.zn_ncl = 0
+}
diff --git a/packages/ludic.zones/tests/zones_test.ludic b/packages/ludic.zones/tests/zones_test.ludic
new file mode 100644
index 00000000..1206f13b
--- /dev/null
+++ b/packages/ludic.zones/tests/zones_test.ludic
@@ -0,0 +1,52 @@
+# zones_test.ludic - discs merged into clusters (near players one, far ones two, a player leaving
+# splits the chain), inside or not, how far to the nearest edge, and the radius a fog gives
+import "ludic.zones"
+import "ludic.base"
+program ZonesTest {
+  numbers float
+
+  test "two near players are one cluster, two far apart are two" (zones_st: mut ZonesState) {
+    zones_reset(zones_st)
+    zones_set(zones_st, 0, 0.0, 0.0, 200.0)
+    zones_set(zones_st, 1, 300.0, 0.0, 150.0)
+    zones_merge(zones_st)
+    expect_eq(zones_clusters(zones_st), 1)
+    expect_eq(zones_cluster_of(zones_st, 0), zones_cluster_of(zones_st, 1))
+    expect_eq(zones_cluster_n(zones_st, 0), 2)
+    expect(zones_cluster_r(zones_st, 0) >= 325.0)
+    zones_set(zones_st, 1, 1000.0, 0.0, 150.0)
+    zones_merge(zones_st)
+    expect_eq(zones_clusters(zones_st), 2)
+    expect(zones_cluster_of(zones_st, 0) != zones_cluster_of(zones_st, 1))
+  }
+
+  test "a player leaving the middle of a chain splits it" (zones_st: mut ZonesState) {
+    zones_reset(zones_st)
+    zones_set(zones_st, 0, 0.0, 0.0, 200.0)
+    zones_set(zones_st, 3, 350.0, 0.0, 200.0)
+    zones_set(zones_st, 5, 700.0, 0.0, 200.0)
+    zones_merge(zones_st)
+    expect_eq(zones_clusters(zones_st), 1)
+    zones_clear(zones_st, 3)
+    zones_merge(zones_st)
+    expect_eq(zones_clusters(zones_st), 2)
+    expect(zones_cluster_of(zones_st, 0) != zones_cluster_of(zones_st, 5))
+  }
+
+  test "inside, the distance to the nearest edge, and nothing set is everywhere" (zones_st: mut ZonesState) {
+    zones_reset(zones_st)
+    expect(zones_contains(zones_st, 5000.0, 5000.0))
+    expect(zones_nearest(zones_st, 5000.0, 5000.0) == 0.0)
+    zones_set(zones_st, 2, 100.0, 100.0, 150.0)
+    expect(zones_contains(zones_st, 200.0, 100.0))
+    expect(not zones_contains(zones_st, 300.0, 100.0))
+    expect(zones_nearest(zones_st, 200.0, 100.0) == 0.0)
+    expect(Math.abs(zones_nearest(zones_st, 350.0, 100.0) - 100.0) < 0.001)
+  }
+
+  test "a player's radius: past the fog, never under the least, the horizon with none" (zones_st: mut ZonesState) {
+    expect(zones_radius(0.0) == ZONES_NO_FOG)
+    expect(zones_radius(30.0) == ZONES_LEAST)
+    expect(zones_radius(500.0) == 540.0)
+  }
+}