What are the API usage limits?
Each API user has the ability to make 86,000 requests per day. There is a max steady state average of 1 request per second. Bursts of 5 requests in a second are allowed as long as steady state average does not exceed 1 per second. These limits can be increased upon request.
What is the max resolution of the browse imagery?
16 meters
Can response geometries be returned in other formats?
Unfortunately the ArcGIS JSON is the only supported returned format. There are a few good libraries in different languages that can be used to make a conversion. For example:
How long does it take for a new image collection to be available in the API?
Usually somewhere between 90 and 120 minutes from the time of collection to when the image is available in the catalog API.
Can this API be easily used with Leaflet and OpenLayers?
Yes, both open source web mapping libraries have plugins that allow for integration.