Guides How to use OS Finding Aids

How to use OS Finding Aids

All of National Collection of Aerial Photography's (NCAP) catalogued finding aids to Ordnance Survey (OS) aerial photography of Scotland are available on our website. 

 

These finding aids show geographic coverage of mapping surveys over several decades. They allow you to locate and identify aerial photographs of your area of interest.

 

Once you have identified frames of interest, you can order copies through our Scan on Demand service.

1: OPEN OUR LEGACY WEBSITE

Navigate to the legacy image viewing platform. 

Log in with your NCAP subscription if you have one. This will allow you to zoom and pan images and view all digitised finding aids. 

Tip: You do not need a subscription to see if there is coverage for your area of interest held in finding aids, however you will need one to view individual finding aids. 

Legacy Website - Map View

A screenshot of a digital map of Edinburgh Park and Sighthill. In the top right of the map is a box titled ‘Search tools’ with the options ‘See images in this area’ and ‘See finding aids in this area’. The box has been circled to highlight it.

2: Zoom to your Area of Interest

Using the search bar or the map tool, find the general area of interest. 

Click 'See finding aids in this area', which has the small airplane icon. 

A screenshot of a list of aerial survey sorties for which NCAP has finding aids – annotated maps showing where photos were taken. The list details the sortie number, date and relevant finding aid. A sortie number has been circled to highlight it.

3: REFINE YOUR RESULTS

You are presented with a list of all sorties, linked to the grid square of 10-minutes of latitude and longitude in which your area of interest is located.

You will be able to further refine your search results by date, using the fields provided.

Tip: You can order this list chronologically by clicking on 'Date'. Likewise, you can sort by sortie reference number. 

If any images from this sortie have already been digitised you should see them presented at the bottom of the page. These can be purchased directly through the Legacy Website.

To examine the finding aids in greater detail, you will need a website subscription.

4: EXAMINE FINDING AIDS

Some data is provided for you in the list, but you will need to review each sortie finding aid to see if there is exact coverage offered to meet your needs. 

Use the 'Zoom image' feature to open, zoom and pan each image in higher resolution.

Tip: Right-click on a sortie which looks to be of interest and select 'Open link in new tab' so you do not lose your place on the results list. 

A new tab will open, showing our record for the selected sortie. Since sorties and finding aids often covered more than one location, there may be more than one page available to view. A thumbnail for each page is shown. The map on the right-hand side of the page shows the grid squares covered during the mission.

A portion of an Ordnance Survey map of the Shetland Islands. It has been marked with coloured lines indicating the routes of aerial survey sorties. A colour-coded key providing information about each sortie is at the bottom.

5: Finding Aid Formats

Ordnance Survey finding aids are available in two formats:

  • 1:63,360 (1 inch to 1 mile) base maps showing the flight line of the survey aircraft and the ground footprint of the photography in differently coloured boxes.
  • 1:50,000 (2 cm to 1 km) flight diagrams showing the flight line of the survey aircraft and the centre point of each photograph by means of unique symbols.
An OS flight diagram for the year 2002. It is a black and white map annotated with 3 intersecting lines showing flight paths. The lines are studded with dots showing where photos were taken. A dot indicating frame 63 has been circled to highlight it.

6: IDENTIFY A PHOTOGRAPH

Zoom and pan the finding aid until you find your area of interest. The locations and coverage of photographs are shown by boxes or strips drawn on the map. See if these fall over your area of interest. 

Tip: Your area of interest may appear on more than one page, so remember to check all of the thumbnails for each mission.

The photograph frame number is usually shown in the box. Sometimes frames are only shown at intervals along a strip. 

Tip: For full coverage of 062 from this sortie, you would likely order frames 061 to 063, inclusive.

A black and white map of the Torran Rocks in the Hebrides. A symbol key at the bottom left records film numbers, altitudes, focal lengths and dates for sorties recorded on the map. The film numbers have been highlighted with a blue circle.

7: Identify a Film

Since several flights, all flown on different dates, often appear on the same finding aid, it is important to know the details of the specific flight that your selected photograph was taken. Pan to the data box in the corner of the finding aid, where each flight is listed along with its corresponding symbol or colour. Take a note of the relevant film reference.

Tip: Also listed in this box are the dates each survey flight was undertaken, along with the mean altitude of the aircraft above sea level and the focal length of the camera lens used during the flight.

A black and white map of Iona and Mull in the Hebrides. A symbol key at bottom left records film numbers, altitudes, focal lengths and dates for sorties recorded on the map. The altitudes and focal lengths have been highlighted with a blue circle.

8: Calculating Heights, Focal Lengths and Scales

Photo scale depends on the altitude of the aircraft and the focal length of the camera lens. OS aerial photography was usually taken with cameras of 6-inches (153mm) or 12-inches (306mm) focal length.

Where the data box records the focal length (FL) as 12-inches, the photo scale has the same value as the height. Therefore a photograph taken with a focal length of 12-inches, from an altitude of 7,000 feet, has a nominal scale of 1:7000.

Where the data box records the focal length as 6-inches, the photo scale has double the value as the height. Therefore a photograph taken from an altitude of 7,000 feet, with a focal length of 6-inches, would have a nominal scale of 1:14000.

9: TAKE NOTES

When you find maps and drawn squares which provide coverage for your area, take note of the exact frame numbers you wish to order. 

To order image you must provide the sortie and frame number. 

Tip: If you are ordering just a few images from one finding aid, there is a text box on the image page where you can easily input frame numbers for the sortie you are viewing. These will help populate the order form. 

10: ORDER IMAGE(S)

As suggested above, you can record the frame numbers of the photographs that you require in the notepad area. Then click 'Order Images'.

Our online order form will open in a new tab. You can select the resolution of copy you require, provide your contact details and tell us how you wish to use the image before submitting your order.

Online Order Form

11: CAN'T IDENTIFY THE RIGHT IMAGE?

If you are unable to decide which frame covers your area of interest, we offer 72ppi Research Copies. These allow you to check the coverage and quality of a photograph before ordering a high-resolution copy.

The finding aids may not always be 100% accurate, so we recommend that you also order copies of the frames before and after the one you have identified, to make sure you cover the area you want.

12: NO COVER OF YOUR AREA OF INTEREST?

If the finding aid shows no photography of your specific area of interest, close the tab and return to the page of search results. Select another mission from the list and repeat steps 3, 4 and 5.

Once you have examined all of the relevant finding aids, you have completed your search.

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