Ch. 10 Ch. 10 Putting Maps Together: Map Putting Maps Together: Map

OverlayOverlay

John Van AukenJohn Van Auken

DefinitionsDefinitions

• Map OverlayMap Overlay

• Sieve MappingSieve Mapping

• Co-registrationCo-registration

• Boolean OverlayBoolean Overlay

4 steps to Map Overlay4 steps to Map Overlay

• Determine the inputsDetermine the inputs

• Get the dataGet the data

• Reference the maps to the same Reference the maps to the same projection/coordinate systemprojection/coordinate system

• Overlay the mapsOverlay the maps

Determining the InputsDetermining the Inputs

• Knowledge-Driven – when we use the Knowledge-Driven – when we use the ideas and experience of experts in ideas and experience of experts in the field to determine what criteria to the field to determine what criteria to useuse

• Data-Driven – use is made of any Data-Driven – use is made of any data available to suggest which data available to suggest which criteria should be usedcriteria should be used

Getting the DataGetting the Data

Go get it.Go get it.

Referencing the DataReferencing the Data

• Translation – move the origin of the Translation – move the origin of the coordinates used in map B to the same coordinates used in map B to the same point in map Apoint in map A

• Scaling – change the scale on both X and Y Scaling – change the scale on both X and Y axes axes

• Rotation – when x and y are not parallel to Rotation – when x and y are not parallel to the corresponding axes in map A, the corresponding axes in map A, coordinates may need to be rotated to coordinates may need to be rotated to correct for this. correct for this.

Referencing the DataReferencing the Data

An affine transformation is a specific class An affine transformation is a specific class of coordinate transformation in which the of coordinate transformation in which the only changes allowed are translation, only changes allowed are translation, scaling, and rotation, and where no other scaling, and rotation, and where no other distortion of the coordinates may occur. distortion of the coordinates may occur.

Matrices can be used to accomplish co-Matrices can be used to accomplish co-registration using an affine registration using an affine transformation. transformation.

Overlaying the MapsOverlaying the Maps

Overlay the maps using a GIS. Overlay the maps using a GIS.

This is easier in a raster environmentThis is easier in a raster environment

Problems with Boolean Problems with Boolean OverlayOverlay• It is assumed that the relationships really It is assumed that the relationships really

are boolean. are boolean. • It is assumed that any interval or ratio-It is assumed that any interval or ratio-

scaled attributes are known without scaled attributes are known without significant measurement error. significant measurement error.

• It is assumed that any categorical attribute It is assumed that any categorical attribute data are known exactly. data are known exactly.

• It is assumed that the boundaries of the It is assumed that the boundaries of the discrete objects represented in the data discrete objects represented in the data are certain, and recorded without any are certain, and recorded without any error. error.

Alternatives to Boolean Alternatives to Boolean OverlayOverlayFavorability Functions Favorability Functions • Indexed Overlay – when you add values Indexed Overlay – when you add values

together to obtain a favorability score together to obtain a favorability score for each location.for each location.

• Weights of Evidence – makes use of Weights of Evidence – makes use of conditional probability….since B has conditional probability….since B has occurred, what is the chance of A? occurred, what is the chance of A?

• Model-Driven Overlay Using Regression Model-Driven Overlay Using Regression – uses regression techniques to – uses regression techniques to calibrate a model linking favorability to calibrate a model linking favorability to each of the other criteria thought to be each of the other criteria thought to be involved.involved.

Questions Questions

• What is Boolean overlay? And what What is Boolean overlay? And what are the problems associated with it?are the problems associated with it?

• Describe the three techniques used Describe the three techniques used to co-register data. to co-register data.

• What are 2 alternatives to Boolean What are 2 alternatives to Boolean overlay?overlay?