GIS is an indispensable tool for solving complex spatial problems and making informed decisions. However, even seasoned professionals can encounter setbacks due to preventable mistakes. Whether you're just starting out or have years of experience, it’s crucial to recognize and avoid common errors that can compromise data quality, mislead analysis, or hinder project progress. From overlooking metadata to relying on outdated data or poorly organizing your layers, small oversights can have big consequences. By understanding these 16 mistakes and learning how to prevent them, you can streamline your workflows, improve accuracy, and ensure your GIS projects deliver maximum value. Remember, successful GIS work isn’t just about using the right tools—it’s about applying them thoughtfully and consistently.