Managing Raster Data Using ArcGIS

Question 1

What is a geodatabase model used to catalog, process, visualize, query, and share small to large collections of raster data.

Answer 1

A mosaic dataset

Question 2

Any mosaic dataset that you add to ArcGIS Pro is added as a mosaic layer, and it appears in the Contents pane as a special group layer. This group layer must have at least what three layers?

Answer 2

The boundary, the footprint, and the image layers

Question 3

A mosaic dataset reads all the metadata from the rasters and imagery. It enables what capabilities:

Answer 3

1) Defining extra metadata
2) Defining image-processing functions to be applied to the imagery when the data is accessed
3) On-the-fly processing that applies all required processing to the imagery as it is accessed, removing the requirement to pre-process imagery
4) Dynamic mosaicking that allows overlapping imagery to be merged and fused

Question 4

Mosaic datasets can be accessed and viewed with any license level, but what levels are required to create them?

Answer 4

Standard or Advanced

Question 5

What is the workflow to create and add rasters to a mosaic dataset?

Answer 5

1) In a geodatabase, create an empty mosaic dataset and its schema.
2) Add raster datasets to the mosaic dataset. Datasets can come from many sources, including files, folders, tables, or web services.
3) Modify the mosaic dataset (make updates to the boundary and footprints, add more raster data, and so on).
4) Define and build overviews for the mosaic dataset.

Question 6

Large mosaic datasets can present performance challenges. With raster data, you can optimize the data display and performance using what two mechanisms?

Answer 6

Pyramids and overviews.

Neither method is mandatory, but both help speed the display of a raster dataset.

Question 7

What is a reduced-resolution layer that enhances performance by making copies of the original data at decreasing resolution? They are especially helpful for large datasets.

Answer 7

Pyramids

Question 8

What is a reduced-resolution raster dataset created to increase display speed and to reduce CPU usage?

Answer 8

An overview

Question 9

What are highly recommended because areas where they are not generated may show a wireframe instead of any imagery. This failure occurs when the display can only process a limited number of rasters at one time. (You can change this setting.) You can choose not to create them, or you can choose to generate them for only highly visited parts of the mosaic dataset.

Answer 9

Overviews

Question 10

Created for: Raster datasets

Format: Writes .ovr files—with a few exceptions: They stored externally are read as *.ovr or *.rrd or internally (such as MrSID).

Storage: Stored in a single file next to the source raster dataset and using the same name.

Extent: Each level covers the entire raster dataset and can specify the number of levels to generate.

Answer 10

Pyramids

Question 11

Created for: Mosaic datasets

Format: Written as .tif files.

Storage: By default, stored in a folder next to the geodatabase with a *.overviews extension. Storage location is customizable.

Extent: Each one can cover part of or all of a mosaic dataset. Each level may consist of one or more images.

Answer 11

Overviews

Question 12

Generally, (overviews or pyramids) perform faster than (overviews or pyramids) for each raster within the mosaic dataset. Using (overviews or pyramids) results in greater performance because they are often larger in extent than the source files, so fewer files must be opened.

Answer 12

1) Overviews
2) Pyramids
3) Overviews

Question 13

Build what? When using these raster types or imagery:
1) Raster datasets larger than 3,000 columns
2) Overlapping rasters where mosaic methods will control the order
3) Source rasters that will be processed on the fly at all scales
4) Images other than static preprocessed rasters

Answer 13

Pyramids

Question 14

Build what? When using these raster types or imagery:
1) Reprocessed tiled imagery, such as orthophoto quads
2) Edge-joined (non-overlapping) imagery that will not be affected by changing mosaic methods
3) Imagery that will be processed on the fly, and parameters and mosaicking methods that will not be changed

Answer 14

Overviews

Question 15

When building complex mosaic datasets, you can build __________ on the source rasters and then build ________ only where they are needed. This strategy has several advantages:
1) Takes advantage of mosaic methods and on-the-fly processing
2) Reduces the number of overviews
3) Helps when viewing a mosaic dataset without overviews

Answer 15

1) pyramids
2) overviews

Question 16

Where are overviews stored?

Answer 16

Overviews are generated and stored, by default, in a folder next to where the mosaic dataset resides. This folder has the same name as the geodatabase with the .overview extension.

You can also control where the overviews are stored. For example, if they are not maintained within the geodatabase, you might prefer to store them with the source rasters. Use the Define Overviews tool to define the output location for your overviews before generating them. In addition, you can use several compression methods to control the space required to store the overviews.

Question 17

Generate what only in the following situations:
1) You want to use the mosaic dataset for visualization purposes (at different scales of interest).
2) You have no time constraints when working with large mosaic datasets.
3) You are creating a simple mosaic dataset with fewer datasets.

Answer 17

overviews

Question 18

Why are overviews not automatically built?

Answer 18

Overviews are not built automatically for several reasons:

1) They take additional space and time, and you may want to build them at your convenience.
2) You may want to add additional data before you are ready to build the overviews.
3) You may want to modify the default mosaic method after the data is added and before the overviews are built. (By default, they are built using Closest To Center).
For example, building overviews using By Attribute would allow you to build overviews by choosing the most recent data or data with the least cloud cover.
4) You may want to modify the default properties of the overviews, such as the storage location or format, or even constrain the area in the mosaic dataset for which they are built.
5) You may want to use lower-resolution imagery you already have or a service instead of generating overviews.

Question 19

When should you generate overviews? Determine the extent of flooding and visualize the movement of water.

Answer 19

Generate overviews because you need to visualize at different scales.

Question 20

When should you generate overviews? Quickly identify evacuation routes during a flood emergency.

Answer 20

Do not generate overviews because time is limited.

Question 21

When should you generate overviews? As part of a site selection process, identify where and how emergencies might occur.

Answer 21

Generate overviews because you will visualize the locations and extents of multiple types of emergencies.

Question 22

When should you generate overviews? Quickly analyze hazards and their potential impacts (plumes, earthquakes, and so on).

Answer 22

Do not generate overviews because time is limited.

Question 23

When should you generate overviews? Determine slope to locate potentially flooded areas.

Answer 23

Generate overviews because you need to display the mosaic dataset to locate potential low-lying areas.

Question 24

You have gathered many overlapping images representing an urban area with many buildings. For each scenario, choose the most appropriate mosaic rule to control the order of rasters for visualization of the data.

You are mapping building footprints and need buildings that appear to stand straight.

Answer 24

Closest To Nadir

Question 25

You have gathered many overlapping images representing an urban area with many buildings. For each scenario, choose the most appropriate mosaic rule to control the order of rasters for visualization of the data.

You want to see the sides of buildings so that you can identify features such as entrances and windows.

Answer 25

Closest To Viewpoint

Question 26

You have gathered many overlapping images representing an urban area with many buildings. For each scenario, choose the most appropriate mosaic rule to control the order of rasters for visualization of the data.

Because you want to see little distortion in the images, you want to view the centers of the images.

Answer 26

Closest to Center

Question 27

You have gathered many overlapping images representing an urban area with many buildings. For each scenario, choose the most appropriate mosaic rule to control the order of rasters for visualization of the data.

You want to see the most recent imagery.

Answer 27

By Attribute

Question 28

You have gathered many overlapping images representing an urban area with many buildings. For each scenario, choose the most appropriate mosaic rule to control the order of rasters for visualization of the data.

You want to control the viewing of buildings from each side.

Answer 28

Closest To Viewpoint

Question 29

When is it appropriate to manage your raster datasets using a mosaic dataset?

Answer 29

You want to use small to large collections of your raster data for managing, visualizing, performing many geoprocessing analyses, and querying.

Question 30

List the advantages of organizing raster data in a mosaic dataset.

Answer 30

A mosaic dataset allows you to perform the following tasks:
1) Store, manage, view, query, and share small to vast collections of lidar data.
2) Perform raster-level operations on lidar data.
3) Complete on-the-fly processing.
4) Display data faster at any scale.

Question 31

When you add a mosaic dataset to ArcGIS Pro, it is added as a mosaic layer that appears in the Contents pane as a special group layer with a minimum of three layers. What are these layers called and what does each display?

Answer 31

Boundary, Footprint, and Image. The Boundary layer displays the boundary of the mosaic dataset, the Footprint layer displays the footprints for each raster within the mosaic dataset, and the Image layer controls the rendering of the mosaicked image.

Question 32

What are rules for ordering overlapping rasters when viewing the mosaicked image called?

Answer 32

Mosaic methods

Question 33

T/F: Any modifications you make in the Image layer will not affect the properties of the mosaic dataset.

Answer 33

True

Question 34

T/F: You have gathered 59 county-level, 1-meter IKONOS images. You would like to create a mosaic dataset using these images. However, you want to exclude areas of cloud cover. It is appropriate to generate overviews in this scenario during the process of adding rasters to the mosaic dataset.

Answer 34

False

Question 35

In the process of creating a mosaic dataset, why is building overviews considered an optional step?

Answer 35

Building overviews takes time when you are working with large mosaic datasets.

Question 36

You have obtained three large raster datasets with three different resolutions. What is the best method to manage these raster datasets?

Answer 36

Create a single mosaic dataset and add the three raster datasets to the mosaic dataset.

Question 37

You have obtained raster data for a portion of Laguna Niguel, California. Using this data, you have built a mosaic dataset. Which of the following options would you use to order rasters within a mosaic dataset based on a defined metadata attribute and then display the data in ArcGIS Pro?

Answer 37

Change the mosaic method from the layer properties of the mosaic dataset.