I have precipitation data points separately as a shapefile in one layer and I also have a polygon shapefile from where the precipitation data was collected.

How do I join these two layers and compute a precipitation map within the polygon boundary?

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  • "A spatial join can assign the attributes of the polygon directly to the attribute table of the output point file. Right-click the point file and choose Joins and Relates > Join. Select the option to join data from another layer based upon spatial location. Choose the grid polygon layer and select the option to give the attributes of the polygon to each point that falls inside". Source: Point in Polygon Selection and Attribute Assignment, Author timothy_hales-esristaff – Taras Nov 6 '18 at 7:30
  • You can have many points in one polygon? If so you can intersect Points with polygon, summary statistics per polygon id (or Dissolve if you have advanced license) and join back to the polygons. – BERA Nov 6 '18 at 8:05

When no other information is available, the most robust method would be to take the average precipitation inside your polygons. This can be done with the Spatial join tool of ArcGIS with the JOIN_ONE_TO_ONE option. If some polygons do not include any points, you can also use the "CLOSEST" matching option.

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