Overlay Analysis - Point in Line, Point in Polygon, Line in Polygon, Polygon on Polygon

What is Overlay Analysis?

Overlay means placing one layer on top of another in GIS to see how they are related.

Imagine putting a transparent sheet of roads on top of a map of forests — that's overlay!

1. Point in Line

• Points are single locations (like bus stops).

• Lines are long features (like roads or rivers).

"Point in Line" means checking which points lie on or near a line.

✅ Example:
You have a map of bus stops (points) and roads (lines).
You check which bus stops are on which roads.

2. Point in Polygon

• Polygon is an area (like a city, park, or forest).

• Point in Polygon means checking which points are inside an area.

✅ Example:
You have schools (points) and a map of city boundaries (polygons).
You want to see which schools are inside which city.

3. Line in Polygon

• Now you're checking which lines pass through or are inside areas.

✅ Example:
You have rivers (lines) and forests (polygons).
You want to find which rivers flow through forests.

4. Polygon on Polygon

• You have two sets of areas and want to see how they overlap.

✅ Example:
You have agricultural land (polygons) and flood zones (polygons).
You want to find which farmlands are in flood-prone areas.

 Why is this important?

Overlay analysis helps us:

• Understand how different map layers interact,

• Plan better (like building hospitals where people live),

• Protect the environment (like stopping construction in forests),

• Study problems (like flood risk areas).

Summary Table:

Type	What it checks	Example
Point in Line	Which points lie on/near lines	Bus stops on roads
Point in Polygon	Which points are inside areas	Schools in cities
Line in Polygon	Which lines cross through areas	Roads through forests
Polygon on Polygon	How two area layers overlap	Farms in flood zones