I have a shapefile of the country. I need to select only percentage of that polygon for demonstration purposes. As an example, how to select 60% of polygon?
I am using ArcGIS 9.3.
You cannot "select" only a part, you need to divide your polygon to create 2 new geometries before.
There is a tool for this within the parcel fabric of ArcGIS 10.1 standard and advanced licence, but I don't know if it is available with 9.3 (maybe with survey analyst). I cannot check for this anymore.
Otherwise there is the Split Polygon by area for ET geotools.
This solution will give you a 'roughly right' answer, but it may be useful for a quick turn task that doesn't require an exact answer.
Step 1 - Run the Create Fishnet (Data Management) tool using your polygon as the template to establish an extent (i.e. x min, x max, y min, y max). Use your discretion for defining the number of rows/columns keeping in mind that the smaller your fishnet polygons are the closer you will be to your target goal (60% in this case).
Step 2 - Run the Clip (Analysis) tool to reduce the fishnet to the area of your polygon
Step 3 - Determine how much area is (in this case) 60% of your polygon (polygon area * 0.6)
Step 4 - Use a Search Cursor to loop through the clipped fishnet adding the area of each polygon until you get to 60% (The size of your polygons in the fishnet will determine how close to 60% you can get using this method). Be sure to capture the Unique ID of the polygon that gets you to 60% (e.g. if the sum of the first 10 polygons gets you to 60%, you'll need the OBJECTID/UID of the 10th polygon to use in a selection in the next step).
Step 5 - This step is only required if you are running this in code or model builder. If you are doing this in ArcMap, skip this step. Run the Make Feature Layer tool create a temporary layer that will allow you to select individual features in a feature class.
Step 6 - Use the Select Layer by Attribute tool to select all polygons whose OBJECTID/UID field is <= x where x is the OBJECTID/UID of the polygon that got you to 60% (in the example above, x would be 10).
Again, this is not the best solution, but it may get you by in a crunch.