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Map scripts in [maps/\*.asm](../tree/master/maps/) declare new objects—NPCs, item balls, Berry trees, etc—with the `object_event` macro. But you can't have more than 15 `object_event`s in one map. ([GoldenrodCity.asm](../blob/master/maps/GoldenrodCity.asm) reaches this limit, and four other maps nearly do with 14 `object_event`s.) Turns out this is an easy limit to increase.
Edit [constants/wram_constants.asm](../blob/master/constants/wram_constants.asm):
```diff
; wMapObjects:: ; d71e
PLAYER_OBJECT EQU 0
-NUM_OBJECTS EQU 16
+NUM_OBJECTS EQU 18
```
And edit [wram.asm](../blob/master/wram.asm):
```diff
- ds 40
+ ds 6
wMapObjects:: ; d71e
wPlayerObject:: map_object wPlayer
wMap1Object:: map_object wMap1
wMap2Object:: map_object wMap2
wMap3Object:: map_object wMap3
wMap4Object:: map_object wMap4
wMap5Object:: map_object wMap5
wMap6Object:: map_object wMap6
wMap7Object:: map_object wMap7
wMap8Object:: map_object wMap8
wMap9Object:: map_object wMap9
wMap10Object:: map_object wMap10
wMap11Object:: map_object wMap11
wMap12Object:: map_object wMap12
wMap13Object:: map_object wMap13
wMap14Object:: map_object wMap14
wMap15Object:: map_object wMap15
+wMap16Object:: map_object wMap16
+wMap17Object:: map_object wMap17
wMapObjectsEnd::
wObjectMasks:: ds NUM_OBJECTS ; d81e
```
That's it! We just added space for maps to define 17 total `object_event`s. (Plus the player object, making 18 total.) So you could, for example, add two more NPCs to make Goldenrod City feel busier.
Let's look at how it works. `wMapObjects` is an array of `map_object` structs, one for each possible object (including the player). You can see what data is stored for each `map_object` in the macro definition in [macros/wram.asm](../blob/master/macros/wram.asm):
```asm
map_object: MACRO
\1ObjectStructID:: db
\1ObjectSprite:: db
\1ObjectYCoord:: db
\1ObjectXCoord:: db
\1ObjectMovement:: db
\1ObjectRadius:: db
\1ObjectHour:: db
\1ObjectTimeOfDay:: db
\1ObjectColor:: db
\1ObjectRange:: db
\1ObjectScript:: dw
\1ObjectEventFlag:: dw
ds 2
ENDM
```
This is all the same data that gets declared by the `object_event` macro, defined in [macros/scripts/maps.asm](../blob/master/macros/scripts/maps.asm):
```asm
object_event: MACRO
;\1: x: left to right, starts at 0
;\2: y: top to bottom, starts at 0
;\3: sprite: a SPRITE_* constant
;\4: movement function: a SPRITEMOVEDATA_* constant
;\5, \6: movement radius: x, y
;\7, \8: hour limits: h1, h2 (0-23)
; * if h1 < h2, the object_event will only appear from h1 to h2
; * if h1 > h2, the object_event will not appear from h2 to h1
; * if h1 == h2, the object_event will always appear
; * if h1 == -1, h2 is treated as a time-of-day value:
; a combo of MORN, DAY, and/or NITE, or -1 to always appear
;\9: color: a PAL_NPC_* constant, or 0 for sprite default
;\10: function: a OBJECTTYPE_* constant
;\11: sight range: applies to OBJECTTYPE_TRAINER
;\12: script pointer
;\13: event flag: an EVENT_* constant, or -1 to always appear
db \3, \2 + 4, \1 + 4, \4
dn \6, \5
db \7, \8
shift
dn \8, \9
shift
db \9
shift
dw \9
shift
dw \9
ENDM
```
`wObjectMasks` is likewise an array of mask bytes, one for each possible object. If the mask is −1, the object is hidden.
Basically, the `object_event` structs in the ROM get copied into the `map_object` structs in RAM, so there needs to be enough space in RAM for all of them. And each new object needs 17 bytes—16 for its `map_object` (count them), and one for its mask—so we had to use 34 of the unused bytes in that `ds 40`.
If you wanted to allow an 18th object, you would have to find 17 bytes of unused space here and there in the same `SECTION` as `wMapObjects` and `wObjectMasks`. Which is not difficult; if you scroll down to the "`map scene ids`" and "`fight counts`", they both have large chunks of unused space afterwards (`ds 49` and `ds 100`).
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