You can use the resolution table and values. No resolution value is needed for vector graphics. If images consist of pixels, resolution values are needed. Illustrator does not use visuals like Photoshop. When you open the image in Photoshop program, you can have 300 ppi, but when you enlarge the visual size in the Illustrator program, the resolution value decreases. You can see the value used from the Link panel to find the dimensions of the images. Vector graphics do not use the resolution value whether they are created externally or in an illustrator.
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