Chapter 6

Spatial Joins

Which county has most earthquakes?

1. County data layer2. Earthquake data layer3. No common field between layers

Spatial Joins• A spatial join is based on the

location of spatial features rather than common field

• Spatial join may create new attributes, such as count or distance in the output data

Spatial Join Join LayerTarget layer

Output Layer

Spatial Join Counties showing the frequency of earthquakes

Spatial JoinsSpatial join can be used to find:

• The closest feature to another feature. • What features in one layer are inside another feature. • What intersects a feature.

Spatial join creates a new layer from two input layers by combining both sets of attributes.However, it does not combine the features to the target layer

Which watershed has the highest number of septic systems?

Watershed Septic System

Color coded Watershed

Count field shows the # of septic system in each watershed

Spatial Join (Point to point)

2. Closest point to the target layer including the distance

Two options1. How many points are

closest to it including the summary statistics of closest points

Which Hospital is closest to most cities?

Spatial Join (Point to point) Use Option 1 without any summary:

Which hospital is the closest to most cities?

No distance field in the output layer

Option 1 add only the Count field in the output layer showing the number of cities that are closest to each hospital

Which hospital is the nearest to most cities?

Which hospital serves most people?

Spatial Join (Point to point) Example: Total number of people served by each hospital

In this case you have to use Summarized under Option1

Spatial Join (Point to point) Example: Total number of people served by each hospital

Summarized option will give summary statistics on each numeric field including the count(# of cities)

Spatial Join (Point to point) Example: Total number of people served by each hospital

This hospital serve most of the cities

This hospital serve most of the people

Which town is farthest/closest from a hospital?

Which town is farthest/closest from a hospital?

Use option 2

Each town features gets name of closest hospital and the distance.

Spatial Join: Point to point-Distance

Get the closest or farthest city by sorting the distance

Example: Which counties are within a watershed

Same county will fall in more than one watershed, as a result duplication will occus in count and also in summary statistics!!

Spatial joinNever use the unprojected data for distance calculation!

You will not only get wrong distance but wrong selection as well !!