Join

The Join tools answer the same need in two ways: your features are missing information that exists in another layer, and you want it on them.

Use a spatial join when the two datasets have no field in common and only their positions relate them. Use an attribute join when they share a key, such as a municipality code or a parcel reference.

Start here

Spatial join

Attaches the attributes of a join layer to each of your features, based on where they sit. Give each incident the district it happened in, each tree the parcel it grows on, each shop the census tract around it.

Parameter	What to set
Input layer	The features you want to enrich. They keep their geometry.
Join layer	The layer whose attributes you want to copy over.
Predicate	How the two must relate: intersects (they touch or overlap at all), within (your feature is inside the join feature), contains (your feature holds the join feature).
How	Inner keeps only the features that matched. Left keeps every input feature, with empty values where nothing matched.

Start with intersects and a left join, look at how many rows came back empty, then tighten from there. Any geometry type works on both sides.

Attribute join

Copies fields from a table onto your features where a key matches, with no geometry involved. This is how you put census statistics onto boundary polygons, or a price list onto a layer of outlets.

Parameter	What to set
Input layer	The layer to enrich.
Join layer	The layer or table holding the values.
Target field	The key field on your layer.
Join field	The matching key field on the other side.
Fields	Which fields to bring over. Copy only what you need, so the result stays readable.
How	Inner keeps only matched features, left keeps all of them.

The join is one to one: if several rows share the same key, the first one wins. When a join returns nothing, the key fields are almost always the cause. A code stored as text on one side and as a number on the other will not match, and neither will codes that differ by a leading zero.

All the tools

Tool	What it does
Spatial join	Attaches attributes from a join layer to each input feature, based on a spatial relationship: intersects, within or contains. Inner or left join, any geometry type.
Attribute join	Attaches attributes from a join layer where a key field matches, without using geometry. One to one, the first matching row wins.