Arcmap - Prevent Polygon fills from leaking into the background

[TadhgLynch]

As shown in the image certain polygons are 'leaking' from its boundaries , this seems to occur to certain shapefiles when cut across by the display port as shown in the example. I have looked online and similar problems have happened where a 'dirty polygon' is leaking on other software but none I could use to solve this. The GCS is GCS_Unknown which doesn't match the project and I'm unsure as to whether that is the issue. It doesn't allow for conversion in any case. Please let me know if you have any ideas. Thanks!

[ChristopherCounsell · Accepted solution]

You mean the orange area?

Try:

• Defining a coordinate system. If you don't know the original, you can ask the source. Maybe create a copy of the feature class and define one based on your basemap, if it is aligning correctly.
• Convert to a feature class in a file geodatabase. 
• Run the Repair Geometry tool

[TadhgLynch]

Thanks ! the repair geometry was what I was looking for