1. Aerial photography All (most) of our base data map layers have come from air photos
… imap

2. Traditional surveying: triangulation
Theodolite
Triangulation station
Geodetic station

3. Early days: Boston, from Tethered Balloon (1860)
Development of aerial photography before airplanes

4. Air photos for reconnaisance from fighter planes and pigeons
Word War I:
Air photos for reconnaisance from fighter planes and pigeons
Balloons and kites were easy to shoot down, but pigeons were not.
Small cameras were attached to the birds and a timer was set to take pictures every 30 seconds as it flew

5. Oblique photos from mountain peaks

6. Early topographic mapping from mountain peaks: Canadian Rockies, 1890
Photo-topography led by Edouard Deville, was used until 1950
Early topographic mapping from mountain peaks: Canadian Rockies, 1890

7. Since 1945, all our topographic mapping is done from aerial photography:
Air photos enabled a huge reduction in fieldwork costs, and an increase in how quickly and accurately large areas could be mapped
Athabasca Glacier, 1958

8. Photos are not ‘planimetric’: there are distortions
“Tip, tilt and swing”
Relief distortion
Radial distortion

9. There are two distinct branches of aerial photography:
Photogrammetry:       "the science of obtaining reliable measurements from photos"
Photo interpretation: "the identification and extraction of meaning of objects"
Photogrammetry needs a minimum of
5 known point locations per photo

11. Accessing air photos

12. Index maps 1936-1950 microfiche, >1950 paper

13. Flight Reports organized by year

14. Flight map 1970_B-006-FI-70_16000

15. Photo library – Victoria, BC

16. Individual photos

17. Stereoscopes – 3D imagery

18. Stereo – 3D to create elevations

19. ORTHOPHOTOS
Once corrected, and georeferenced, photos can be used for topographic mapping and as a mapping layer, with  map data overlain on top.
A photograph that has been corrected and is 'planimetrically correct' is known as an  orthophoto (e.g. as in google maps, pgmap or BC- imap ).

20. Map layer features are identified using:
Image interpretation
Map layer features are identified using:
Shape
Pattern
Size
Tone
Colour
Shadow
Texture
Site
Time

21. Provincial photography is generally redone about every 10+ years
City photography more frequently: 3-5 years PG

22. Time sequence, PGmap: http://pgmap.princegeorge.ca/pgmap.html
Aerial photos still use film, but these are then scanned
and input into digital photogrammetric software for processing.
Photos can be purchased as scanned TIF files

23. Digital photography: Terrasaurus aerial photography, Williams Lake