How to Find Airphotos

Finding airphotos for an area of interest is often a complicated and time-consuming process. Please contact the staff of the Map and Airphoto Collection if you need help. Our goal in providing assistance is to teach the user how to find airphotos and to thereby engender independent use of the collection.




Step 1. Determine the Relevant 1:50,000 NTS Map Sheet(s)

If you know the 1:250,000 map sheet number you can go direct to the flightline index (step 3), but you can save yourself some work by first determining the 1:50,000 map sheet number.

There are several ways of determining the 1:50,000 map sheet number:

1. If your site is in Alberta, start with a map of Alberta that will allow you to focus in on the area of interest and determine the NTS map sheet number.

2. If you know generally where the area is, consult the topographic maps held by the Map and Airphoto Collection. We have complete coverage of Canada between the 1:50,000 and 1:250,000 scales.

3. If you know the legal description, consult the topographic maps. Legal descriptions are given in the form S  T  R  W  M (eg. 12 14 8 W 4) where S is the section number, T is the township number, R is the range number, W stands for west, and M is the meridian number. Township nu mbers increase as you go north and range numbers increase as you go west from one meridian to the next.

4. If you know the place name, try Canada's Official Geographical Names Web Site. When it retrieves your name of interest, click on the name to get more information, including the NTS map number.




Step 2. Determine the Airphoto Sets for the 1:50,000 Map Sheet

This step makes use of the database of sets of airphotos that have coverage within each 1:50,000 NTS map sheet.

The result of searching the database is a number of sets of airphotos. For each set there is a small table listing

• the call number (ie, the label for the set of airphotos),
• the scale,
• the year the airphotos were taken,
• the type of photo (eg, panchromatic, colour, infrared, etc.)
• the 1:50,000 map sheet number,
• the extent of coverage of the 1:50,000 map sheet
  (scant = 0-10%, partial = 10-90%, complete = 90-100%),
• the airphoto agency, and
• any notes.

Note that the results returned from the database are not necessarily in order by call number (by 1:250,000 map sheet and then by scale). For completeness work through the entire set of results that are returned. The maximum number of airphoto sets that will be returned is 250. If your search retrieves 250 items there are probably more, and you may want to try some method of narrowing your search.

There are three methods of searching the airphoto database:

1. If your site is in Alberta, start from a map of Alberta that will allow you to focus in on the area of interest, find the NTS map sheet number(s), and determine the relevant sets of airphotos.

2. When you know the 1:50,000 map sheet number.

3. Keyword search. This permits you to combine the map sheet number with information such as scale or extent of coverage. It is probably not reliable for other purposes. You could search the notes for a place name, but the results are likely to be incomplete.




Step 3. Identify the Individual Airphotos on the Flightline Indexes

The flightline indexes are a miserable set of indexes to work with. They consist of photocopies of topographic and other maps at various scales. The photocopies, which were usually supplied with the airphotos, are often very poor quality photocopies of photocopies.

Unfortunately the use of the flightline indexes cannot be avoided. They are the only information available that shows where the individual airphotos were taken.

The flightline indexes are in large floppy map binders. Flightline indexes for the Calgary area have been organized separately in four brown binders that are arranged by the year the airphotos were taken. The other flightline indexes are arranged first by the 1:250,000 NTS map number and then by the scale.

On most flightline indexes, the airphotos held by the University of Calgary Library are marked in green. But on some index maps it may instead be noted that the Library holds all airphotos of the set.

If you know the sets of airphotos that have coverage for your 1:50,000 map sheet (from step 2 above), you can restrict your work to those flightline indexes. If you only know the 1:250,000 map sheet number, you will need to work through all the flightlin e indexes for that map sheet number.

It can be a real help to bring in the 1:50,000 NTS map sheet so that you can compare the flightline index with the topographic map sheet. In the case of Calgary, a city map is useful. The maps will help to determine which airphotos are wanted, and once the airphotos have been retrieved they will help to identify features on the airphotos.

Airphotos are usually designated by flightline number and an airphoto number for that flightline. Some index maps may have only one flightline number or they may have numbered the airphotos consecutively across several flightline numbers. In this case o nly the airphoto numbers will be needed. Other airphoto indexes will have several flightline numbers with overlapping airphoto numbers, and it is necessary to have both numbers to retrieve the appropriate airphotos.




Step 4. Retrieve the Airphotos of Interest

The airphoto sets are stored in brown document boxes, labelled with the call number. Sometimes there is more than one call number in a document box. Sometimes there is more than one box for a set of airphotos, in which case the flightline numbers and/or airphoto numbers are written on the document boxes.

The document boxes are stored in the back room on movable compact shelving. Airphoto sets with restricted circulation are mixed in with the main collection. The airphoto sets are ordered first by the 1:250,000 map sheet number, then by the scale and the n by the year. Please be careful in moving the shelving so that you do not crush a co-worker (or competitor) between the shelves.

Knowing the call numbers of the airphoto sets of interest and the airphoto and flightline numbers, you can retrieve the boxes of airphotos of interest to you. (If the box is not on the shelves, you may find it in the work area.)

Individual airphotos usually have the airphoto numbers and flightline numbers marked on them, but the numbers can be anywhere around the edge of the airphoto, and can often be hard to find. Each airphoto has the call number stamped on the back.

When you take airphotos out of the boxes, please mark the location with the strip markers to enable staff to more speedily refile the airphotos. It is better if you do not refile the airphotos - the collection gets out of order too quickly as it is. If the airphotos you want are not in the appropriate box, please ask staff for assistance, as there are several places they might be.

Airphotos are not marked with a north arrow. To determine which direction is north, take two consecutive airphotos, look for common features, and lay them out so they overlap. The flightline index will indicate the direction of the flight, as will the i ncreasing numbers of the airphotos, and from the index you can then determine which direction is north.

Working from the flightline indexes may only give an approximate idea of the airphoto numbers that you want. When you retrieve the airphotos, check the features against a topographic map or a city map to ensure they cover the correct area. Distinctive f eatures such as roads, cutlines, waterbodies, etc. can often make this task quite straightforward, but areas with little in the way of distinctive features can make this process very difficult. When that happens follow along a flightline until you come t o a feature you are sure of and then try to work back to the area of interest.

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