008] Global Mapper - Saving Online Maps for Offline Use

I don't have enough time to write a long post today, so I'll share a quick but very useful tip instead.

When you use online maps in Global Mapper, there is one significant drawback: every time you pan or zoom, the software has to connect to the map server to reload the area. This can be quite frustrating and time-consuming. In such cases, you can convert the map for offline use. By loading saved images instead of connecting to a server, you can significantly reduce your working time.

Let's get started.

Step 1: Loading Your Workspace

First, open the workspace you saved in the previous session.

Step 2: Checking the Loading Lag

On this screen, try zooming in while keeping all layers off except for World Imagery.

Tip: You can zoom in and out using the mouse wheel, and pan by clicking and dragging with the mouse wheel button.

Do you notice how the map reloads every time you zoom? If you zoom in beyond the screen size and pan, you'll see that it takes time to load new areas as well.

Step 3: Exporting the Online Map

Now, let's save the online map separately for offline use.

1. Select the World Imagery layer in the Control Center.
2. Right-click and select Layer - EXPORT.

When the "Select Export Format" window appears, choose JPG and click OK. (You can select other formats depending on your specific needs.)

Step 4: Configuring Export Options

When the JPG Export Options window appears, configure the settings as shown below and click OK.

Sample Spacing: This defines how many meters represent one pixel.

• For example, if you enter 1, 1, then 1x1m of the online map becomes 1 pixel.
• If you enter 5, 5, then 5x5m of the online map is saved as 1 pixel.

The smaller the number, the higher the resolution, but the file size will be larger and downloading will take longer. Since World Imagery uses an international server, setting it to 1x1 might take 3-4 minutes or more for the current map. (Using V-World API is much faster, often taking less than a minute. I highly recommend applying for and using the V-World API.)

Metadata File Formats to Generate: Make sure to select World File (.jgw) and PRJ (Projection) File. Since a standard JPG image doesn't "know" its actual geographic location, GIS programs use these JGW and PRJ files to place the image in the correct coordinates.

Step 5: Saving the File

Choose your save location, enter a name, and click OK.

A progress bar will show the process of downloading the map from the server. Once finished, the window will disappear.

Step 6: Loading the Offline Map

Now, let's load the map we just saved. Go to File - Open Data File(s)...

Select the JPG image from the location where you just saved it and click OK.

You will now see the "Offline Map" (오프맵) added to the bottom of your Control Center.

Conclusion: Speed vs. Resolution

Now, try turning off the original World Imagery layer. Since we downloaded it at a lower resolution this time, the image might look blurry when you zoom in too far. However, if you zoom in, zoom out, or pan, you'll notice that the screen transitions at a much faster speed than before.

The map used in this example is about 6x6km. If you download it at 1x1m resolution, it becomes a 6,000 x 6,000-pixel image, which is quite large. Higher resolution isn't always better. It is best to download at an appropriate size, considering the final output size for your reports or projects.

That’s it for today!