When you import vector graphics, After Effects automatically rasterizes them. However, if you want to scale a layer that contains vector graphics above 100%, then you need to continuously rasterize the layer to maintain image quality. You can continuously rasterize vector graphics in layers based on Illustrator, Flash SWF, EPS, and PDF files. Continuously rasterizing causes After Effects to rasterize the file as needed based on the transformation for each frame. A continuously rasterized layer generally produces higher-quality results, but it may render more slowly.

Shape layers and text layers are always continuously rasterized.

When you apply an effect to a continuously rasterized layer, the results may be different than when you apply the effect to a layer without continuous rasterization. This is because the default rendering order for the layer changes. The default rendering order for a layer without continuous rasterization is masks, followed by effects, and then transformations; whereas the default rendering order for a continuously rasterized layer is masks, followed by transformations, and then effects.

Whether or not you continuously rasterize, if you view and render a composition using Best Quality, After Effects anti-aliases (smooths) the vector graphics.

You cannot open or interact with a continuously rasterized layer in a Layer panel. This means that you can’t paint directly on a continuously rasterized layer. However, you can apply the Paint effect, and you can copy and paste paint strokes from other layers.