Compare Historical Aerial Images of One Block
Aerial images can show visible land-use changes on a block, but image dates, coverage, and scale matter. Record those details so observations remain traceable and appropriately limited.
Choose a clear block and image set
Define the block by its bordering streets and note whether your study includes alleys or adjacent parcels. Find aerial images from more than one date that cover the same area. Record the repository, image identifier, flight or capture date, and any scale or resolution information provided.
Check whether a displayed date refers to image capture, scanning, or catalog entry. If the date is unclear, mark it as uncertain and seek the source's catalog notes before building a chronology around it.
Orient and compare carefully
Use stable features such as street intersections, rail lines, or large buildings to align views. Aerial images may differ in angle, crop, sharpness, or season. Those differences can hide features or alter how open land and vegetation appear.
Make a list of visible features for each date: building footprints, paved surfaces, open lots, trees, or street patterns. For example, a later image may show a larger roof area, suggesting an addition or replacement. Permits, parcel records, or construction plans can help determine which explanation is supported.
Separate observation from interpretation
Describe what the image visibly contains before assigning a use. A roof footprint does not identify a building's occupants or function. A bare lot does not prove it was vacant throughout the year. Land-use changes require supporting records when the image alone is ambiguous.
When comparing footprints, note the image quality and any areas obscured by shadows or trees. Avoid precise measurements unless you have an appropriate scale and account for image distortion. A visual comparison is often enough to identify a question for further research.
Keep the source trail intact
Build a small table with image date, source, identifier, block coverage, observation, and limitation. Cite each image directly and keep an unaltered copy where permitted. If you crop or adjust contrast for display, disclose that and retain the original reference.
Finish by summarizing the visible changes across the sampled dates and naming what other records could confirm. The result is a reproducible account of what the aerial evidence shows, without claiming more than the images can establish.
Spotted something we should look at? Suggest a correction.