Geodeziya, kartografiya, geografiya

How do I select the imagery I'll need?
Now that you have defined the classes you want to map, it is necessary to select appropriate imagery that will allow you to accurately define these classes. Selecting appropriate satellite imagery is, more often than not, a subjective task. The selection is often limited to the resources that are available. If the project budget is limited you may be restricted to using free or inexpensive imagery, which in turn affects the level of information that can be extracted for the map. Ultimately, this may require that the needs assessment be adjusted to reflect the practical limitations of the project.
The spatial detail of the final maps will dictate the required resolution of the basemap and this will significantly limit the list of possible image types that can be used. For example, if you were interested in identifying individual trees you would need a few fine resolution satellite images or aerial photographs. If, on the other hand, you wanted to create a global land cover map you would look for a much coarser resolution. The selection of an appropriate image resolution is somewhat of an art and experience will indicate the limits of available image types. One rule of thumb that can be used as a rough guide to select an appropriate resolution is that the area of the minimum mapping unit should be ten times the surface area represented by a single pixel. In other words, if you had a minimum mapping unit of 1 hectare a Landsat Thematic Mapper image with a 30 meter resolution would be appropriate since one hectare equals approximately 11 pixels (10,000m/30m x 30m). Perhaps a better way to get a feel for the level of detail that can be extracted from a remotely sensed image is to view it on a computer display and zoom and roam around the image to see how well individual features can be identified. If you can see it on the screen there is a good chance it can be properly classified.
The specific classes you are looking for will also have some effect on the type of image data you are looking for. For example, some sensors are better designed for collecting information about aquatic environments and others are more suitable for specific terrestrial environments. This is an area where advice from someone with experience classifying similar features would be useful. Some additional information is available in the guide titled What you need to know when searching for satellite imagery.