Data\<year>\.These settings (and Reset View) are shared by the Map and Trends tabs, so what you pick on one is still picked on the other. Reset View puts everything back: the map zoom and position, any selected airport or line, the Network, Aircraft and Compare to settings, and the Month (newest).
Pick a month to see every route as a line between airports; thicker lines mean more flights per week. Hover an airport and everything it connects to lights up, with a list of its connections on the right. Hover a line to see that route's flights. Click to keep a selection, click empty map to clear it. Scroll to zoom and drag to pan.
Compare to: pick a second month and both tabs show what changed between it and the Month you have selected. Green lines/bars are routes added (flown in the Month, not in Compare to), red dashed lines or bars were dropped, amber changed frequency by a full flight per week or more, and grey are about the same. On the Map, the side panel lists them and hovering an airport shows its added and dropped routes. On Trends, a diverging bar chart shows city pairs added and dropped by count, and the list below names them. Network and Aircraft apply to both months. Set it back to None to return to the normal view.
Average weekly flights for every month in the archive, stacked by aircraft type or by network (Split by), narrowed by Network and Aircraft. Under it, Routes added and dropped: a diverging bar chart shows the count of city pairs added (green, up) and dropped (red, down) per month compared with the previous month in the archive. The list below names them for the chosen Month against the month in Compare to (or the previous month if Compare to is None). The chosen Month is highlighted; click a bar or month header to choose it. A flight that runs only part of a month counts for that fraction.
Which routes each aircraft type flies. The list on the left has every type in the Month with its average weekly flights, how many routes (city pairs, both directions together) and airports it serves; click one to see its routes on the right, busiest first. The Network and Aircraft settings narrow it, and Compare to adds the other month's figures: a type can be new or gone, and each route shows added, dropped or a change of a full flight a week or more.
Airlines only publish a schedule for the current month, so this tab looks further ahead by asking Google Flights for this airline's nonstop flights on one route and reading the aircraft type for each. Type the From and To airport codes (for example DFW and LAX), pick the Month (this month or any of the next five), then press Search. It checks every day of that month, one month at a time to keep the number of searches down (about 30). A search pauses a few seconds between dates, so a month takes a few minutes; Stop ends it and keeps what was found. Each route and month you search is one saved search, so a search never covers more than about 31 dates.
Every search you run is kept under Saved searches: the route, the Month, how many of that month's days have been searched (for example 14 of 31 in amber means the search was stopped part-way), and when it was last searched. Results are saved in the GoogleFlights\ folder. Click a search to select it. Open (or a double-click) shows each date, where the shaded rows have a widebody flight with its flight number (for example AA614), and Back returns to the list. Search and Update both scan every day of the month again: Update for the selected search, and Update All for every saved search one after another (it asks first, because a long list means many requests and can take a while; Stop ends it and keeps what was found). If a later scan finds a widebody added, dropped or swapped on a date, the Change column says so and what it was before. Move Up and Move Down reorder the selected search, and you can also drag one by its ⠿ handle. Remove deletes the selected search and its dates (it asks first). A saved search is also removed automatically once its month has ended (the January searches go on February 1). Reordering and removing are saved straight away.
This is not an official Google service, so it can stop working or be limited if Google changes its page or sees too many requests. If searches fail three times in a row the tab stops and says so; wait a while and try again. Google shows the aircraft an airline currently plans to fly, which can change before the date.
Data\ and reads it.Data\ — use after dropping in a file yourself.parsed\ and reused.Data\ in Explorer.