Canadian airspace is the region of airspace above the surface of the Earth within which Canada has jurisdiction. It falls within a region roughly defined as either the Canadian land mass, the Canadian Arctic or the Canadian archipelago, and areas of the high seas. Airspace is managed by Transport Canada and detailed information regarding exact dimensions and classification is available in the Designated Airspace Handbook which is published every fifty-six days by Nav Canada.
The "Canadian Domestic Airspace" includes all of Canada and extends out over the Pacific, Arctic, and Atlantic oceans. It is broadly divided into the "Northern Domestic Airspace" (NDA) and the "Southern Domestic Airspace" (SDA).
There are three main differences between the two areas, the most important of them being that the NDA is designated as a "standard pressure" region while the SDA is an "altimeter setting" region. This means that pilots operating in the SDA will calibrate their altimeters to atmospheric pressure according to information available at airports and through weather services. Conversely, in the NDA, pilots calibrate their altimeters to 29.92 inches of mercury (101.3 kPa) regardless of the actual atmospheric pressure. This is done because weather information is not available for all areas of the far north, so it is better that all pilots use a standard setting in order to avoid collisions.
Another major difference between the NDA and SDA is that magnetic declination is not used in the NDA. Because the North Magnetic Pole is close to the NDA (and was formerly within it), magnetic declinations can be very large and changeable from year to year. This is further complicated by the fact that magnetic north wobbles every day in an elliptical path as much as 50 miles (80 km). For these reasons, "true" tracks are always used in the NDA while magnetic tracks are frequently used in the SDA for convenience.
The final difference between the NDA and the SDA has to do with the location of Class A airspace in each region. This is explained in more detail below.
Canadian Domestic Airspace is the second-largest air navigation service by volume of air traffic in the world, after the United States
There are seven classes of airspace in Canada, each designated by a letter (A through G).
Airspace classes A through E are controlled. Class F can be controlled or uncontrolled. Class G is always uncontrolled. Airspace is managed by Transport Canada and detailed information regarding exact dimensions and classification is available in the Designated Airspace Handbook which is published every fifty-six days by NAV CANADA.
Some control zones have unique procedures because of terrain or air traffic demands. These procedures are published in the Canada Flight Supplement. From the supplement "Class E* All high level controlled airspace above FL600 within the SCA, NCA and ACA. Also, low level airways, low level fixed RNAV routes, CAEs, transition areas or CZs established without an operating control tower may be classified Class E airspace." So uncontrolled airports like Sarnia (CYZR) and others may appear to be miss-characterized as control zones since the Canadian Air Regulations (CARs) define a CZ as "controlled airspace that is so specified in the Designated Airspace Handbook (DAH) and that extends upwards vertically from the surface of the earth up to and including 3,000 feet AGL, unless otherwise specified" in that handbook.
However, this apparent conflict is resolved since the DAH is specifically authorized to define airspace classification. The CARs definition of controlled airspace is "...within which air traffic control service is provided;". So when air traffic control is not provided it appears it should not be a control zone. The DAH defines Class G airspace as "Airspace shall be classified G if it has not been designated A, B, C, D, E or F." There is actually no definition of "uncontrolled airspace" other than that, so by inferred definition CYZR is controlled airspace below 700 ft to 5 nmi beneath a Class G, transition airspace out to 15 nmi). The 700 ft is the base of this overlaying Class E transition airspace which is controlled up to FL125. DAH also defines "Class B, C, D or E equivalent" airspace but that specifically refers MTCAs which are military terminal control areas.
Bottom line is the CARs definition of CZ and controlled airspace specifically allows the DAH to further define certain "Class E uncontrolled airports" as a control zone as long as they have at least one navigation aid and an instrument approach procedure that originates in Class E transition controlled airspace.