Raster Analysis Methods

Raster overlays, key operations and techniques.

Clip

Often our data covers more area than needed, we can clip it to reduce the data volume.

• Clip Raster: cuts raster down to a bounding box.
  • Max N/S & E/W extent of another layer (vector or raster) or manually defined.

Reclassify

When data is more complex than needed.

• Reclassify: creates a new output based on a classification scheme.
  • Reassign values or simplify data to reduce data volume

Mosaic

Sometimes the data comes in parts that need to be combined

• Mosaic: Combine multiple raster data sets into one.
  • There are multiple approaches we can use.

Mosaic

Sometimes the data comes in parts that need to be combined

• Mosaic: Combine multiple raster data sets into one.
  • There are multiple approaches we can use.

Often used to merge multiple satellite images

Proximity Analysis

Sometimes, we’re interested in looking at spatial relationships using raster data.

• Euclidean Distance: use this tool to calculate distance from the nearest feature or raster layer.

Raster Overlay

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

• Easy, efficient overlay
  • Key advantage of the raster data model
• We have a few tools we can use for this

Weighted Overlay

Weights inputs for suitability analysis or risk assessment.

• Inputs must be discrete numbers
• Manually define weights and scale

Weighted Overlay

Weights inputs for suitability analysis or risk assessment.

• Discrete outputs

Raster Calculator

More general and flexible than weighted overlay.

• Outputs are more straightforward
  • Because inputs are more explicit
• Can do weighted overlay among other tasks

Raster Calculator

More general and flexible than weighted overlay.

• Continuous output

TopHat Question 1

This tool allows you to define equations using raster layers as variables.

• Weighted Overlay
• Raster Calculator
• Reclassify
• Mosaic

Zonal Statistics

Calculate statistics by region.

• The zone can be either a raster or vector layer.
• Zonal Statistics as Table generates a table containing multiple statistics by zone.

Surface Analysis

These tools are designed to analyze elevation surfaces.

• Slope: calculates the slope of a terrain surface
  • The angle in degrees from a cell to it’s “lowest” neighbor

Surface Analysis

These tools are designed to analyze elevation surfaces.

• Aspect: calculates the direction a slope is facing
  • North, southeast, west northwest, etc.

TopHat Question 2

The euclidean-distance tool lets you calculate the slope and aspect of a raster layer.

• True
• False

Raster Functions

ArcGIS Pro has an extensive toolkit of tools for more complex analyses.

• Many are beyond the scope of intro-level GIS

Hydrologic Modelling

The Hydrology toolset can be used to calculate stream flow.

1. Use a DEM as an input
2. Fill “sinks”
3. Calculate flow direction
4. Run flow accumulation

Hydrologic Modelling

The Hydrology toolset can be used to calculate stream flow.

1. Use a DEM as an input
2. Fill “sinks”
3. Calculate flow direction
4. Run flow accumulation

DEM Input

Hydrologic Modelling

The Hydrology toolset can be used to calculate stream flow.

1. Use a DEM as an input
2. Fill “sinks”
3. Calculate flow direction
4. Run flow accumulation

Accumulated stream flow output

Calculate NDVI

You can calculate NDVI directly in Arc

• Just give the red and near infrared bands from a satellite image
  • e.g. Landsat8: Red (4), near infrared (5)

Image Classification

Supervised or unsupervised classification methods

Image Classification

Supervised or unsupervised classification methods

TopHat Question 3

This group of raster tools allows us delineate streams and drainage basins from a DEM.

• Hydrology Toolset
• Image Classification
• Kernel Density
• NDVI