Zoning

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In a zoning game the player doesn’t build houses, shops, or factories; they mark land for each use, and the simulation fills it. In SimCity each zone scores its type’s demand plus a local term and rolls against the score on a visit, growing one level or declining^1,2.

Games

Game	Year	How	Note
SimCity	1989		a zone's score is its valve plus land value (residential) or nearness to the center (commercial), and growth is a roll against it

Every claim about this mechanic, by game (3)

SimCity 1989	One visit in eight (every visit, for an empty residential zone), a zone takes a score: its type's valve plus a local term. The residential term is (land value − pollution) × 32, held to 0–6000, minus 3000; the commercial term is its 8×8 block's `ComRate`, 64 minus 4 × the block's distance from the city center, so from 64 down to −64; the industrial term is 0. An unpowered zone scores −500 whatever its valve.	Code
	A zone grows if its score is above −350 and (score − 26380) exceeds a random signed 16-bit number; failing that, it declines if its score is below 350 and (score + 26380) is under a second one. The numbers are uniform over −32768 to 32767, so growth comes with chance (score + 6388) / 65536 per evaluation, about 10% at a score of 0 and 17% at a residential zone's highest, 5000. An unpowered zone declines with chance 6887 / 65536, about 10.5%. A commercial zone whose trip failed can't grow; one that made no trip can.	Code
	Growth adds one level at a time and stops at each type's top: a residential zone below 40 population (levels 16, 24, 32, 40), commercial below 5, industrial below 4. A residential zone doesn't grow where its block's pollution is above 128, and a commercial zone grows only while its population is at most its block's land value / 32, so it can reach one level past that figure. An empty residential zone builds single houses until it has 8, then fills in at level 16 only where population density is above 64.	Code

References

^ a bOne visit in eight (every visit, for an empty residential zone), a zone takes a score: its type's valve plus a local term. The residential term is (land value − pollution) × 32, held to 0–6000, minus 3000; the commercial term is its 8×8 block's ComRate, 64 minus 4 × the block's distance from the city center, so from 64 down to −64; the industrial term is 0. An unpowered zone scores −500 whatever its valve.CodeMicropolis (SimHacker/micropolis)
How we know
```
248  if ((CChr9 == FREEZ) || (!(Rand16() & 7))) {
```
micropolis-activity/src/sim/s_zone.c lines 248–251 at c98f6b0 · upstream ↗
```
211    zscore = CValve + locvalve;
```
micropolis-activity/src/sim/s_zone.c lines 209–212 at c98f6b0 · upstream ↗
```
178    zscore = IValve + EvalInd(TrfGood);
```
micropolis-activity/src/sim/s_zone.c lines 177–179 at c98f6b0 · upstream ↗
```
581  if (Value > 6000) Value = 6000;	/* Cap at 6000 */
```
micropolis-activity/src/sim/s_zone.c lines 569–600 at c98f6b0 · upstream ↗
```
537      z = 64 - z;
```
micropolis-activity/src/sim/s_scan.c lines 529–539 at c98f6b0 · upstream ↗
```
292  if (z > 32)
```
micropolis-activity/src/sim/s_scan.c lines 277–296 at c98f6b0 · upstream ↗
Checked against the evidence by its author, an AI model, 2026-10-21.
Checked by a second AI model, 2026-10-21.
In the claim ledger
^ a bA zone grows if its score is above −350 and (score − 26380) exceeds a random signed 16-bit number; failing that, it declines if its score is below 350 and (score + 26380) is under a second one. The numbers are uniform over −32768 to 32767, so growth comes with chance (score + 6388) / 65536 per evaluation, about 10% at a score of 0 and 17% at a residential zone's highest, 5000. An unpowered zone declines with chance 6887 / 65536, about 10.5%. A commercial zone whose trip failed can't grow; one that made no trip can.CodeMicropolis (SimHacker/micropolis)
How we know
```
254	(((short)(zscore - 26380)) > ((short)Rand16Signed()))) {
```
micropolis-activity/src/sim/s_zone.c lines 253–264 at c98f6b0 · upstream ↗
```
214    if (TrfGood &&
```
micropolis-activity/src/sim/s_zone.c lines 214–222 at c98f6b0 · upstream ↗
```
1221    i = 32767 - i;
```
micropolis-activity/src/sim/s_sim.c lines 1216–1223 at c98f6b0 · upstream ↗
```
47	return ((next % ((SIM_RAND_MAX + 1) <<8)) >>8);
```
micropolis-activity/src/sim/rand.c lines 44–48 at c98f6b0 · upstream ↗
Checked against the evidence by its author, an AI model, 2026-10-21.
Checked by a second AI model, 2026-10-21.
In the claim ledger
^Growth adds one level at a time and stops at each type's top: a residential zone below 40 population (levels 16, 24, 32, 40), commercial below 5, industrial below 4. A residential zone doesn't grow where its block's pollution is above 128, and a commercial zone grows only while its population is at most its block's land value / 32, so it can reach one level past that figure. An empty residential zone builds single houses until it has 8, then fills in at level 16 only where population density is above 64.CodeMicropolis (SimHacker/micropolis)revised
How we know
```
305  if (z > 128) return;
⋮
311      return;
⋮
316      return;
⋮
318    return;
```
micropolis-activity/src/sim/s_zone.c lines 300–346 at c98f6b0 · upstream ↗
```
433  return ((CzDen * 8) + 16);
```
micropolis-activity/src/sim/s_zone.c lines 428–453 at c98f6b0 · upstream ↗
```
616	if ((loc >= LHTHR) && (loc <= HHTHR))
```
micropolis-activity/src/sim/s_zone.c lines 605–618 at c98f6b0 · upstream ↗
Checked against the evidence by its author, an AI model, 2026-10-21.
Revised after a check by a second AI model, 2026-10-21.
In the claim ledger

Sources

Code

Wright, Will, Don Hopkins, and Electronic Arts. 2026. “Micropolis: the GPL release of the SimCity engine (SimHacker/micropolis).” Commit c98f6b0. SimHacker/micropolis @ c98f6b0 · licence, all uses

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