Find and download an image
To find a Landsat image of Singapore, you'll use the LandsatLook app to explore the entire database of free Landsat imagery. You want a relatively recent image with minimal cloud cover. To download the image, you'll create a free account for the USGS Earth Resources Observation and Science (EROS) Center, which will allow you to download as much Landsat data as you want.
Landsat imagery can be large. The file you'll download in this lesson has a size of approximately 900 MB. Make sure you have enough disk space on your computer, and enough time to wait for the download, before proceeding.
Create an account
To download Landsat data, you need a USGS EROS account. The account is free, but does require you to give demographic survey data and contact information. If you already have a USGS EROS account, skip to the next section.
- Go to the EROS Registration System.
- Follow the onscreen instructions to proceed through the registration process.
Once you complete your registration, a message is sent to your email address to confirm your registration.
- Click the link in the email to activate your account.
Next, you'll open the LandsatLook Viewer and navigate to Singapore.
- Open the LandsatLook Viewer.
The viewer opens to the default extent of the United States. The Load Images window includes parameters to search for Landsat imagery. The toolbar at the top of the viewer includes buttons for additional options and map controls. First, you'll change the map extent to Singapore.
- On the toolbar, click the Search button.
The Load Images window is replaced by the Search window.
- In the Search window, type Singapore. From the list of results, choose Singapore.
The map extent centers on the city-state of Singapore and the Search window is replaced by the Load Images window. Depending on your browser window size, the windows in the viewer may obscure part of the island.
- Pan the map, and zoom if necessary, to see the entire island.
Most of the island is heavily urbanized, with a few open green areas on the western and central parts of the island. Although the viewer has a scale bar in the lower left corner, at this extent it's difficult to discern Singapore's size relative to other geographic features.
- Zoom out five or six times. Compare Singapore's size to the nearby nations of Malaysia and Indonesia.
- Zoom back to Singapore.
A country the size of a single city presents unique challenges for land use and urban development. Although Singapore has expanded its area by reclaiming land from the sea, its confines remain generally fixed, necessitating stringent planning. But proper planning requires quality data.
Find an image
A real urban planning project would use a variety of data types from many sources. The single image you'll download from the Landsat imagery database will instead serve as a starting point, providing a high quality look at the entire city. Landsat imagery is multispectral, meaning it can be displayed with different bands of visible light to emphasize features such as vegetation, coastlines, or man-made structures. The image will be a good reference to which you can add more specialized data.
- In the Load Images window, for Year, choose to search for imagery between 2011 and the present year.
For accuracy, the image should be relatively recent. You can also search based on days of the year, which is useful for tracking seasonal trends or specific incidents, such as wildfires. For a general reference image, the day of the year doesn't matter.
- For Maximum Cloud Cover, choose 10% or less.
Clouds obscure ground cover and conceal features. Reducing the maximum cloud cover will return results with a clearer view of Singapore.
You can also search for imagery from specific Landsat sensors. All of them capture multispectral imagery, although they use different types of light and have different pixel sizes. They also have different years of operation. The default sensors are Landsat 8 OLI and Landsat 7 ETM+ SLC-off, which are the only sensors operational since 2011. You'll accept the default sensors.
- Click Show Images.
Because new Landsat images are added to the database daily, your search may have returned more images. It may also have a more recent image displayed on the map than in the example images.
All images within the map extent that meet your criteria are returned. Additionally, the most recent images are displayed by default. The Modify Images window, which opened after your search, indicates how many images were returned and how many are currently being displayed. In this example, two out of thirteen images are being displayed, but only one is visible on the current map extent.
- Zoom out until you can see all displayed images.
Depending on the number of active images and the zoom extent of the map, the basemap may disappear (such as in the example shown).
The images cover a larger area than Singapore. Two are currently shown. They are displayed as a mosaic, or a collection of multiple images pieced together. You only want to download one image, so you'll change the display to show one image at a time.
- In the Modify Images window, for Image Display, click Active Date Only.
- Zoom back to Singapore.
The map updates and only the most recent image is shown. This image is the most up-to-date for planning purposes. In this example, however, the most recent image has cloud cover that obscures parts of the city. You'll look at the other images returned by your search to decide the best for download.
- On the Active Date timeline, click the back arrow to display the next most recent image (you may need to wait a few seconds for the image to load).
Alternatively, drag the time slider to view the images.
Your search returned some images that were only partially within the map extent at the time of the search, so some images may not cover Singapore at all.
- Look at each of the returned images.
Some images may have black lines across the image, such as in the image from February 9, 2018:
These black lines are gaps in the sensor data caused by the failure of the Scan Line Corrector in the Landsat 7 satellite. Although these gaps can be filled, an image without significant data gaps is preferred for this lesson.
- From the remaining images, display one with minimal cloud cover that you would like to download.
The image that will be used in the example images is from May 24, 2018:
This image has almost no cloud cover. It's possible that a new image has been added since this lesson was written that shows Singapore with even less cloud cover. Feel free to choose a different image if appropriate.
Download an image
Now that you've chosen an image for your development project, you'll download it.
- At the bottom of the viewer, click Show Metadata.
The metadata table allows you to view information about the images your search returned and add them to your virtual cart for free download. You can choose to look at a table of the images currently displayed on the map or of all images returned by the search.
- Click Show Displayed.
The table changes to list images displayed on the map. You only have the image you want to download displayed on the map, so the table has one entry. The table contains other useful information about the image, such as its percentage of cloud cover.
- Check the box next to the table entry.
If you have multiple entries, use the Acquisition Date column to find the one you want.
- Above the list entry, click Zoom To.
The map zooms to the extent of the corresponding image.
- Confirm that the map is zoomed to the image you want to download. In the table, in the Standard Product column, click Download.
- If prompted, sign in to your USGS EROS account.
A new browser window appears, showing your Item Basket and all scenes pending order from your USGS EROS account. The scene you chose can be downloaded as either a LandsatLook Image or a Level 1 GeoTIFF Data Product. A LandsatLook Image is a PNG image file with no geographic information in its data. A GeoTIFF Data Product contains coordinate information within the image itself. When added to a GIS application such as ArcGIS Pro, a GeoTIFF image will automatically be placed in its coordinate location, ready for analytical use. The GeoTIFF image also contains multispectral bands, allowing you to change how the image looks to emphasize different features on the ground. You'll download the Level 1 GeoTIFF Data Product.
- To the right of the available products for your pending scene, click the download icon.
A window appears, showing your download options and the size of each available download. The Level 1 GeoTIFF Data Product has a file size of several hundred megabytes (the size varies from image to image; the example image is 832 MB). Landsat scenes come in large file sizes and can take a long time to download. Make sure your computer has enough hard drive space before proceeding.
- Next to Level-1 GeoTIFF Data Product, click Download.
- Wait for the download to finish.
The download will probably take more than 15 minutes. You can use your computer for other things while the image is downloading.
You've used the LandsatLook app to search Landsat's vast database of multispectral satellite imagery. You also located and downloaded an image that may be useful raw data for future development in Singapore. Next, you'll open the image in ArcGIS Pro and change its band combination to show Singapore more clearly.
Prepare the image
Previously, you downloaded an image of Singapore taken by a Landsat satellite. Next, you'll prepare the image for analytical use. First, you'll extract the image from the zipped file format it was downloaded as. Then, you'll add the image to a map in ArcGIS Pro and symbolize it by changing its band combination to better show Singapore's urban features.
Unzip the image
As you could tell from the download time, raw Landsat images have large file sizes. The file size is large partly because you actually downloaded a zipped file that contains more than 10 images of the same area, each taken with a different spectral band. Together these images can be combined to create a multispectral image. To view the images, you must unzip the file. You'll also create a folder to store the data.
- Create a folder called Singapore Data in an easy-to-remember location on your computer, such as your Documents folder.
- Locate the downloaded file on your computer.
Depending on your web browser, you may have been prompted to choose where the file would be downloaded to before you began the download. Most browsers download to your computer's Downloads folder by default.
The file is named by its identification code on the USGS website, which is a long string of letters and numbers. The file has the extension .tar.gz, which is a type of file that has been compressed twice instead of just once. You'll need to unzip the contents twice to view the images.
- Right-click the file and extract it to the Singapore Data folder.
The default process to extract files varies depending on your file compression utility.
- Locate the extracted file.
When extracted only once, the file has the same name, except its extension is .tar instead of .tar.gz. Some file compression utilities recognize .tar.gz files and automatically extract them twice.
- If necessary, extract the .tar file.
Once fully extracted, the .tar file contains 12 images (possibly fewer if you downloaded an image from a different sensor) and a text file. Each image has the same name as the original file except for the number at the very end, such as B1, B2, and B3. The B stands for band; each image shows a different spectral band of the same image. The Landsat 8 spectral bands will be discussed in more detail later in the lesson.
- Double-click the B1 image to open it in your computer's default image viewer.
The image is mostly gray, with some visible clouds. Features such as landmasses and oceans are indistinct and difficult to distinguish. Images of a single spectral band tend to look like this, as they cover only a small wavelength of light. To make an image that looks like what the human eye sees, multiple spectral bands are usually combined into a multispectral image.
- Close the image.
Open the image in ArcGIS Pro
To view the individual bands as a single multispectral image, you'll start a new project in ArcGIS Pro. A project contains databases, toolboxes, styles, and other folders that may be useful when making a map.
- Start ArcGIS Pro. If prompted, sign in using your licensed ArcGIS account.
If you don't have ArcGIS Pro or an ArcGIS account, you can sign up for an ArcGIS free trial.
When you open ArcGIS Pro, you're given the option to create a new project or open an existing one. If you've created a project before, you'll see a list of recent projects.
- Under New, click Map.
The Map template creates a project with a default basemap.
- In the Create a New Project window, change the project name to Singapore Development.
By default, the project is saved to the ArcGIS folder, located in your Documents folder. If you want to save the project elsewhere, browse to a different location.
- Click OK.
The project opens and displays a map view. In default ArcGIS Pro configuration, the Catalog pane is to the right of the map. The Catalog pane contains all the folders, files, and data associated with this project. You'll use this pane to establish a folder connection to the Singapore Data folder you created earlier.
If you've used ArcGIS Pro before, your Catalog pane may be in a different place or not visible at all. To show the Catalog pane, click the View tab on the ribbon at the top of the window. In the Windows group, click Catalog.
- In the Catalog pane, click the arrow next to Folders to expand it.
The default folder associated with the project is Singapore Development, a folder that was made when you created the project and which shares the project's name. The folder contains some empty geodatabases and toolboxes but no actual data.
- Right-click Folders and choose Add Folder Connection.
The Add Folder Connection window appears, showing a directory of your computer's files.
- Browse to and select the Singapore Data folder where you extracted your Landsat image.
The Singapore Data folder is added under Folders in the Catalog pane.
- Expand the Singapore Data folder.
The folder contains the 12 individual spectral bands. As you saw earlier, these images on their own show little useful information about the area they cover. To display a single multispectral image that contains all of the bands, you'll add the last file on the list, which ends with MTL.txt. MTL.txt indicates a metadata text file, but it is actually a raster product that has been generated with the information in the metadata file.
- Drag the MTL.txt file (the one with the raster icon) onto the map.
If a window appears, asking to build pyramids for the image, click Yes.
The image is added to the map. It looks darker than the image you previewed on the LandsatLook app, but you can change its appearance to show Singapore more clearly.
Symbolize the image
The image's colors are dark and muted. Additionally, the image has black areas of NoData pixels around the edges of the image to make the image a square grid. You'll change the active spectral bands in the image to show the image with more distinct coloring and symbolize the NoData pixels as transparent to make them disappear from the map.
- In the Contents pane, right-click the multispectral image and choose Symbology.
If you've used ArcGIS Pro before, your Contents pane may be in a different place or not visible at all. To show the Contents pane, click the View tab on the ribbon. In the Windows group, click Contents.
The Symbology pane appears. The Primary Symbology section lists the bands used to display the image (they are also shown in the Contents pane). By default, the Red, Green, and Blue bands are used. These bands cover parts of the light spectrum visible to the human eye and together approximate a natural view of the landscape. For urban development, a view that emphasizes features relevant to the city may be more appropriate. The following table lists each band and what it shows best:
Number Name What this band shows best
Shallow water, fine dust particles
Deep water, atmosphere
Man-made objects, soil, vegetation
Shortwave Infrared 1
Cloud penetration, soil and vegetation moisture
Shortwave Infrared 2
Improved cloud penetration, soil and vegetation moisture
Black and white imagery, crisper detail
Thermal Infrared 1
Thermal mapping, estimated soil moisture
Thermal Infrared 2
Improved thermal mapping, estimated soil moisture
The Red band would emphasize the man-made objects of Singapore's urban environment, while the Near Infrared band would emphasize its coastlines and tight boundaries. The Shortwave Infrared 1 band would also be useful to mitigate the appearance of the clouds in the image.
- In the Symbology pane, change the first band to ShortWaveInfrared_1, the second band to NearInfrared, and the third band to Red.
The image on the map changes automatically.
The coastlines are much more defined, and urban areas appear as distinct brown clusters. Next, you'll hide the NoData pixels by symbolizing them to be transparent.
- In the lower part of the Symbology pane, click Mask and check the Display background value box.
The background, or NoData values, can now be symbolized. The default color for NoData pixels is No Color, which is automatically reflected on the map.
- Close the Symbology pane and zoom to Singapore.
This image gives a decent overview of the whole island, with differences between urban and green areas visible at a glance.
- On the Quick Access Toolbar to the upper left of the application window, click the Save button to save the project.
In this lesson, you searched the vast, 40-year database of imagery captured by Landsat satellites to find one showing the island of Singapore for a potential urban development project. After locating the image, you downloaded it, opened it in ArcGIS Pro, and changed its band combination to better show the city. While no urban development project would use only one image to plan for a city's future, this image (in conjunction with feature layers or other imagery) can provide a good starting point. Additionally, you can run analysis on this image to derive new meaning from what is shown.
You can find more lessons in the Learn ArcGIS Lesson Gallery.