The link graph models the web as a network: each page is a node and each hyperlink from page A to page B is a directed edge A→B. Analysing the link graph reveals which pages are most central (high in-degree), which pages are orphaned (no inbound links), and which clusters of pages are closely related.
For custom crawlers, building a link graph of a target site helps prioritise which pages to scrape first (high in-degree pages are often the most important), identify all reachable pages from a given starting point, and detect crawl traps (pages that link to many others but are linked from nowhere, indicating auto-generated content).
Link graph analysis is also used in SEO research to measure a site's internal linking structure, identify thin-content pages that receive no internal links, and audit redirect chains. Tools like Screaming Frog and Sitebulb crawl sites and visualise the link graph interactively.