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Before adding a legend, you should be sure that the portion of your map that appears on the layout page is what you intend to display in your final product.
- In the insert tab, click the New Layout on the right of the New Map and choose the suitable size.
- in In the insert tab, click the Legend, and drag on the layout to your desired size.
- Move the legend and the map somewhere so that they will be visible on the page.