Vector Analysis Methods

Querying and overlaying vector layers, key operations and techniques.

Vector Analysis Methods

Many operations can be done with vector data.

• Some methods are very similar.
  • Distinctions between methods can be subtle, but important.
  • Can complete the same tasks, but need slight changes to a workflow.
• Typically in GIS there are multiple ways to get the same answers.
  • Some “routes” are just more direct.

Querying Attributes

Finding features of interest based on attributes.

• A good way to reduce data volumes, export queries to new layers
• In ArcGIS Pro you can Select by Attribute
  • Uses SQL (Structured Query Language)
  • Check equality, relative magnitude, etc.
  • Combined with operators: AND / OR

Querying Attributes

Finding features of interest based on attributes.

• If we’re only interested in historic residential buildings:
  • Where “YEAR BUILT” ≤ 1950 AND
    “TYPE” = “Residential”
  • Save as a new layer, won’t have to search through all the objects every time.

Select by Attribute

Sample SQL queries

• Where “SPECIES” = “Pine”
• Where “SPECIES” ≠ “Pine”
• Where “HEIGHT” ≤ 5
• Where “SPECIES” = “Pine” AND “HEIGHT” ≤ 5
• Where “SPECIES” = “Pine” fc0314OR “HEIGHT” ≤ 5

Species	Age	Height
Pine	10	5
Pine	95	28
Oak	200	25
Oak	5	4

Select by Attribute

Sample SQL queries

• Where “SPECIES” = “Pine”
• Where “SPECIES” ≠ “Pine”
• Where “HEIGHT” ≤ 5
• Where “SPECIES” = “Pine” AND “HEIGHT” ≤ 5
• Where “SPECIES” = “Pine” OR “HEIGHT” ≤ 5

Species	Age	Height
Pine	10	5
Pine	95	28
Oak	200	25
Oak	5	4

Select by Attribute

Sample SQL queries

• Where “SPECIES” = “Pine”
• Where “SPECIES” ≠ “Pine”
• Where “HEIGHT” ≤ 5
• Where “SPECIES” = “Pine” AND “HEIGHT” ≤ 5
• Where “SPECIES” = “Pine” OR “HEIGHT” ≤ 5

Species	Age	Height
Pine	10	5
Pine	95	28
Oak	200	25
Oak	5	4

Select by Attribute

Sample SQL queries

• Where “SPECIES” = “Pine”
• Where “SPECIES” ≠ “Pine”
• Where “HEIGHT” ≤ 5
• Where “SPECIES” = “Pine” AND “HEIGHT” ≤ 5
• Where “SPECIES” = “Pine” OR “HEIGHT” ≤ 5

Species	Age	Height
Pine	10	5
Pine	95	28
Oak	200	25
Oak	5	4

Select by Attribute

Sample SQL queries

• Where “SPECIES” = “Pine”
• Where “SPECIES” ≠ “Pine”
• Where “HEIGHT” ≤ 5
• Where “SPECIES” = “Pine” AND “HEIGHT” ≤ 5
• Where “SPECIES” = “Pine” OR “HEIGHT” ≤ 5

Species	Age	Height
Pine	10	5
Pine	95	28
Oak	200	25
Oak	5	4

TopHat Question 1

How many rows in this table would the following query return?

Where “SPECIES” = “Pine” AND “SPECIES” = “Oak”

Species	Age	Height
Pine	10	5
Pine	95	28
Oak	200	25
Oak	5	4
Birch	5	4

TopHat Question 2

How many rows in this table would the following query return?

Where “SPECIES” = “Pine” OR “SPECIES” = “Oak”

Species	Age	Height
Pine	10	5
Pine	95	28
Oak	200	25
Oak	5	4
Birch	5	4

Proximity Analysis

Looking at spatial relationships within or between layers.

• A good way to reduce data volumes, export queries to new layers.
• Multiple options, depending on our needs.
• If we’re only interested in buildings within 1 km of streams:
  • Identify by proximity
  • Save as a new layer, won’t have to search through all the objects every time.

Select by Location

Use to check for spatial relationships such as:

• Containment
• Intersection
• Distance

Geometric Manipulations

These methods create new layers with altered “geometries”. Geometry is a term we use to refer to points, lines, and/or polygons in a vector layer.

Buffer

Create a new Polygon layer based on distance.

• Buffer points, lines, or polygons using a buffer distance or set a field to specify varriable distance.
• Use the Multiple Ring Buffer tool for multi-criteria buffers.

Example From ESRI Docs

Buffer

Create a new Polygon layer based on distance.

• Buffer points, lines, or polygons using a buffer distance or set a field to specify varriable distance.
• Use the Multiple Ring Buffer tool for multi-criteria buffers.

Buffering Tsunami Shelters

Dissolve

Aggregates features.

• Merges objects completely or by attribute(s).
• Can calculate statistics for aggregated regions.
• Useful if our data is more “complex” than we need it to be.

Example From ESRI Docs

Dissolve

Aggregates features.

• Merges objects completely or by attribute(s).
• Can calculate statistics for aggregated regions.
• Useful if our data is more “complex” than we need it to be.

Dissolve Shelter Buffers

TopHat Question 3

This tool allows us to aggregate vector objects in a layer, either completely or by specific attribute values.

• Buffer
• Dissolve
• Select by Attribute
• Merge

Feature Overlay

When we have multiple data layers and we want to combine them to form a new output.

Clip

Cut one layer down to the boundaries of another.

• Useful when we want to focus on a study area
• Does not alter attributes
  • Input layer: our data layer
  • Clip layer: the study area

Example From ESRI Docs

Clip

Cut one layer down to the boundaries of another.

• Useful when we want to focus on a study area
• Does not alter attributes
  • Input layer: our data layer
  • Clip layer: the study area

Input

Clip

Cut one layer down to the boundaries of another.

• Useful when we want to focus on a study area
• Does not alter attributes
  • Input layer: our data layer
  • Clip layer: the study area

Output

Erase

Remove the area of one layer from another.

• Opposite of the clip tool
• Does not alter attributes
• Useful when we want to discard/exclude an area

Example From ESRI Docs

Erase

Remove the area of one layer from another.

• Opposite of the clip tool
• Does not alter attributes
• Useful when we want to discard/exclude an area

Input

Erase

Remove the area of one layer from another.

• Opposite of the clip tool
• Does not alter attributes
• Useful when we want to discard/exclude an area

Output

Intersect

Output where layers overlap and combine attributes.

• Can handle more than two layers at once
• Splits features by overlaps and merges attribute tables
• Merge and parse data at the same time

Example From ESRI Docs

Intersect

Output where layers overlap and combine attributes.

• Can handle more than two layers at once
• Splits features by overlaps and merges attribute tables
• Merge and parse data at the same time

Input

Intersect

Output where layers overlap and combine attributes.

• Can handle more than two layers at once
• Splits features by overlaps and merges attribute tables
• Merge and parse data at the same time

Output

Union

Combine multiple polygon layers, split features where they overlap and combine attributes.

• Similar to intersect, but keeps overlapping areas
• Adds attributes from all overlaps.
• Can handle more than two layers at once.
  • Null values where for new attributes where no overlaps are present.

Union

Combine multiple polygon layers, split features where they overlap and combine attributes.

• Similar to intersect, but keeps overlapping areas

Many More

There are many more vector overlay tools! I have presented some of the the most frequently used tools, but if you have specific use cases you may need others. I can’t cover them all, and I don’t want to overwhelm folks.

TopHat Question 4

Clip and erase remove portions of layer based on location relative to another layer but they do not alter the attribute table.

• True
• False