I have a shapefile with 23 polygons,I want to merge them and get the total area of this big polygon.
But when I used "merge"tool, it only merge polygons but area.
Any ideas about what I should do?
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Use the 'Dissolve' tool.
The Merge tool is for merging multiple feature classes into one new feature class, but still keeping the existing features separate.
The Dissolve tool is for merging features within a feature class into either a single feature, or multiple features based on same attribute values. If the features to be merged are not touching or overlapping, you may want to make sure that you allow multipart features in the Dissolve tool.
NB: If all you want to do is to get the total area, you do not need to merge or dissolve the features at all...
In the attribute table, right click on the 'Shape_Area' column header, then choose 'Statistics' from the pop-up menu.
You will get a few statistics on that field, including the total 'Sum' statistic.
(This alternative is for ArcMap, and for ArcGIS Pro 2.1 and later. ArcGIS Pro earlier than 2.1 does not have this 'Statistics' shortcut. You can do something similar using 'Summary Statistics' (in both ArcMap and Pro), but it's not quite as straightforward.)