008] Global Mapper - Saving Online Maps for Offline Use
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.
"Before we begin, if you missed the previous session, check it out here:"
007] Global Mapper - Viewshed Analysis Including Buildings (Obstructions from Vector Data)
I don't have enough time to write a long post today, so I'll share a quick but very useful tip instead.
Let's get started.
Step 1: Loading Your Workspace
First, open the workspace you saved in the previous session.
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| Global Mapper interface showing the Control Center and an active World Imagery layer with an elevation shader |
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.
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| Zoomed-in view of the World Imagery layer in the Global Mapper Control Center |
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.
- Select the World Imagery layer in the Control Center.
- Right-click and select Layer - EXPORT.
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| Right-click menu in Control Center selecting the Export Layers to New File option |
When the "Select Export Format" window appears, choose JPG and click OK. (You can select other formats depending on your specific needs.)
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| Select Export Format dialog box with the JPG format highlighted |
Step 4: Configuring Export Options
When the JPG Export Options window appears, configure the settings as shown below and click OK.
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| JPG Export Options window showing Sample Spacing set to 5 meters and metadata options checked |
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.
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.
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| Save As dialog box and a progress bar showing the JPG export status at 82% |
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)...
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| File menu highlighting the Open Data File(s) option |
Select the JPG image from the location where you just saved it and click OK.
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| Open file dialog selecting the newly created offline map JPG |
You will now see the "Offline Map" (오프맵) added to the bottom of your Control Center.
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| Control Center showing the added offline JPG layer |
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!
"In the next session, we'll dive deeper into more advanced features. Stay tuned!"
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