Mimic screens for the inSCADA Platform are designed as SVG (Scalable Vector Graphics) files. See What is SVG? The SVG format is a commonly used common standard supported by many graphic design programs. Some of those are;
inkSCAPE (Open Source),
Adobe Photoshop,
Corel Draw,
Microsoft Visio,
AutoCAD.
Figure 1 : SVG Designers
You can use any graphic design program mentioned above to create a mimic screen of your facility or system in the inSCADA Platform.