We present a sketch understanding system for network-like diagrams consisting of symbols linked together. This system employs a novel parser to automatically extract symbols from a continuous stream of pen strokes. The parser uses geometric information to enumerate candidate symbols, and then uses domain knowledge to prune away unlikely candi-dates. The candidates are classified with a novel, domain-independent, probabilistic, feature-based symbol recognizer. Domain knowledge and context are used to correct parsing and recognition errors. To demonstrate our system, we used it to create a sketch-based interface for an electric circuit analysis program.