Where are the borders of the neighborhood? Links to historical maps follow.
The boundaries of Sunnyside
When Sunnyside was laid out by the Sunnyside Land Company in 1891, a plat map showing the streets, lots, and boundaries was submitted to the city. These are the original boundaries.

The far eastern flatiron point was located at Joost Ave and Monterey Blvd (then Sunnyside Ave). The southernmost edge was Havelock Street. The northwest corner was Melrose and Ridgewood Avenues (then Hamburg) and the north/northeast corner stood at Melrose Ave and Congo Street.
On the Border of Awareness
These boundaries have been chipped away at in recent decades–by residents and real estate agents–for reasons that entirely escape this writer. Sunnyside is older than all the surrounding neighborhoods, and has more intriguing history to explore. Why abdicate your own neighborhood?
Real estate agents have at various times have mislabeled houses–edging away at the north and east–stating that houses inside Sunnyside’s borders belong to other neighborhoods (I assume to draw bit more cash). It seems to this observer more honest and more delightful to appreciate Sunnyside’s unique and exciting history–and future.
Through the Years
The Sunnyside Land Company reproduced the original homestead map (with a few misspellings) on their big splashy half-page advertisement in the SF Chronicle announcing their property speculation project in April 1891.

This Dept of Public Works map of Sunnyside from 1912 (with some updates from 1940s) shows the neighborhood extended northward a bit.

The San Francisco Planning Department in the twenty-first century has a different set of boundaries displayed in their SFFind map, somewhat more generous than the original ones, which puts City College, Dorothy Erskine Park, and all of Sunnyside Playground inside the borders. This bit of jiggery-pokery artificially boosts the open-space-to-resident ratio for this neighborhood.

The establishment of City College Ocean Campus in 1937–on the greater part of Balboa Park–removed a 100-acre local public green space that had been previously dedicated in 1910.
Below is how Balboa Park was planned after its dedication, showing ponds and paths. Missing from this depiction is the Ingleside Jail on the park land, which may have had something to do with its slow start as a popular recreation ground. In 1964, the I-280 Freeway would be built on the route of the railroad tracks (black line), taking more land (see peach colored band in modern map above).

Historical Maps
Some links for exploring old maps of San Francisco, including Sunnyside, found on DavidRumsey.com. All linked maps contain a navigation slider embedded in the middle to allow zooming in. It sometimes mysteriously disappears–just click in the left side bar, and it should reappear.

- 1938 aerial photo-map of San Francisco
- 1929 Board of Public Works (MM O’Shaughnessy) San Francisco
- 1924 Rand McNally San Francisco
- 1915 Chevalier Map of San Francisco, gorgeous, colorful, fun
- 1905 Sanborn Insurance Maps (check index; Sunnyside found 715-719)
- 1899 San Francisco Sewer Map (includes streets & topographical lines)
- 1892 HW Faust Map of San Francisco (lots of streets never built, aka “paper streets”)
- 1887 Britton & Rey’s Guide Map of the City of San Francisco (before Sunnyside laid out)
- 1881 Bancroft’s Official Guide Map Of City And County Of San Francisco (also before Sunnyside)