The maps we make use several kinds of coding - shapes, colors, written language (letters), symbolism. A scent-primary map would likely need several layers as well, to separate the kinds of information being offered... and as I'm not sure how exactly scent as a medium can be differentiated as much as color and shape are visually (although maybe different base scents or top notes can be used as symbols, those with this type of mean variations of X, or that type mean in the Y ranges), I will assume that while scent is primary, a secondary sense is allowed. Touch is a good medium, since we have maps with tactile information - braille maps, and also globes where topographic information was included as raised bumps and dips. I think this kind of topographically differentiated map is a good starting point - it lets us get the shape of the environment pretty intuitively, and also lets us use shapes to convey symbolic information.
There are ways to store scent information for later - scratch and sniff stickers or paint is an easy example. There are ways to separate scents into a palette, basic scents building to more complicated ones, to talk about them, recreate them, and so on. This is not often used in casual conversation, since it is primarily of interest to the scent industry, but it gives background for how complicated scent can be, and ways to layer and combine them, or pick them apart.
After all of that, we take our scented paint (in a very wide variety of basic scent components) - and practice that artistic technique known as pointilism. Clever, precise little dabs all working together to create a larger picture. In this case, the different scents, notes, and layers contained in our wide palette of paints. Some base scent that's vegetal and plantlike, can be dabbed here or there with a sharper note to make 'pine', there with a mellower one to make 'moss' (or the reverse, I know it can be done, but I'm not trained).
General climate, topology, ecosystems, can be painted in this fashion either realistically or symbolically (that is, either "pines and oaks" or kinda forest-like or desert-like), as different shadings of color are used on topographic maps. For artificial structures, some symbolism will be needed, certain textures or shapes to mark paths, buildings, residences, towns and cities. But the scents can be layered to give further information - symbolically on a large scale, perhaps paper and ink scents to indicate administration, while a bread scent might mean a restaurant or grocery, as the legends on our maps use little color-blocks. Alternatively, the scents can be used very specifically on a local scale map - here is the bakery with the scent next to and overlapping the oak grove, there is the spice shop, mingling scents with the paper mill.
If the primary sense is scent, then they will be very good at distinguishing such scents - what we use as scratch and sniff paint might be perfectly legible to them even 'inactivated', or might be gently activated - brushing a hand over the map to activate the whole thing at once would give better legibility like we would get from moving to better light. The scents would wear off after a while, they are volatile, but probably not immensely more so than paper maps which fade, or get worn and tear, or just get lost. And they probably can distinguish both the fine distinction of the little dabs of coexisting or mingling scents from the scent-paint, and the overall spatial relation between the areas as the scent changes over the whole map, as well as we distinguish fine color shading or details.
We can use smaller visual maps because we have skill at distinguishing those details, those who use scent maps would have as much skill in their respective specialization - but for us, it might make sense to imagine the map is resized for our noses (as Braille ones are resized for our fingertips), so we can tell things apart. Maybe a poster sized map, where we can physically sweep over it with fingertips and noses to experience this area with these textures and scents is forest and those textures are grasslands, that area with those shapes and layers is city, there is the sharply contained and contrasting scents from buildings used for industry, here are each cuisine's scents from a restaurant area blending and overlapping along that street.
As for scents changing throughout the year, they would probably plan around it - either by using scents that don't change as much for primary identifiers, separating temporary form typical scents - or using them more symbolically. We don't get lost at the greenery on the map when autumn comes and the forest is orange, or snow falls and the streets are white, because we know what the map means and how the land should change.