Leonardo is somewhat lesser known for his astronomy studies, and cannot be considered an astronomer. Much of his studies in this area are often contradictory or said to focus on unimportant events. However, it must be remembered that the telescope was not even in existence during Leonardo's time, though concave and convex lenses were understood and used for vision correction. Some recent claims have been made that Leonardo designed his own telescope, but it seems unlikely he would not have realised the potential for something like this in times of war and made more extensive note of it.
Despite the probable lack of suitable equipment for studying the skies, it was Leonardo who suggested an answer to a question which had been asked since ancient times, that being whether or not the movement of heavenly bodies produced any sound. His reasoning was that they couldn't, and Leonardo even suggested several possible reasons as to why this would be. We now know his conclusions to be correct.
In his work on cartography Leonardo was hardly an innovator. He drew in the traditional style depicting cities, rivers and mountains and drawing them as they were, but with no thought given to the importance of scale. In this way many of his maps overlap into the area of landscape drawings. This is not to say that his work wasn't painstaking and accurate; most certainly it was, but it was also very traditional in style., not something we really associate with Leonardo.
Plan of Imola
The earliest map which it is possible to date is the Plan of Imola drawn in 1502. It is claimed that this is one of the first ever geometric plans drawn of a town. Notes with this work refer to various places in Imola, their distances and directions. Taken with the almost certain date of the work, it is likely this was drawn for strategical reasons.
Arezzo & China Valley
The birds-eye view of Arezzo shows Perugia in the top right-hand corner, Arezzo in the top-left, and Siena at the bottom. It is thought that this map also relates to the same campaign for which the Plan of Imola was drawn.
Leonardo also developed several plans for altering the course of the River Arno which flows through Florence. He carefully mapped the river and in 1503 work was started on digging three new channels to cut off a bend in the river; it was thought this would improve its flow. Several thousand men were involved and it did not please his employer when the project was yet another of Leonardo's failures. Despite this, he was on the right track and a modern project very closely resembles his plans.