Desert Travel
-three roads nearer the edges, one along the coast, and two at the inland border
-camel caravans travel the farthest and do not often stop between cities at smaller towns
-jinn lead caravans that can take carts and more people between towns and cities on hardened sand, payment is required to continue after each settlement
Jinn vs. Slaves
The difference between jinn and slaves is, first, that slaves are human, while jinn are restrained beings of magic.
Second, jinn are only found in the desert. They do not do well beyond its borders.(there might be other mythological critters in similar positions elsewhere in the world, or that live under their own power even within the desert, dunno yet, do we :P)
Third, anyone can own a slave provided they have the money to buy one or the law on their side to keep an indebted under their power. Jinn are owned by the city government and act, generally, as civil servants, for the good of the many. Some are entrusted as life servants to individuals by way of a status symbol(just as often achieved through bribery of officials as it is genuinely meant, there does have to at least be a sort of good reason for it, even if bribery happens).
Fourth, slaves have a chance to escape slavery through hard work, running away(and not getting caught), or being favoured. Or, if they are indebted, managing to work off the debt. Jinn remain servants and outside the system of citizenship in every city they inhabit, with no chance of becoming something more.
Fifth, the standards for keeping slaves are generally better established and enforced than those for jinn. They are both required to be given the minimal neccessities of life: shelter, food and water, but a slave might also be given a slight wage. Jinn are rarely given currency. A slave being mistreated does have legal recourse and might even gain something by speaking with the right person. A jinn being mistreated is just going to have to live with it. A slave that misbehaves may be punished as their owner sees fit, provided the owner keeps within the limits set out by law. A jinn that misbehaves is usually out of luck.
Most small towns don't abuse their jinn. It's the larger cities where bad blood festers or individual contracts that are the worse danger.
Both jinn and slaves would be the first to suffer during economic stress or drought or food shortages.
Both occupy the bottom rung of society.
Some poorer people might choose to enter slavery voluntarily if it means better living conditions or the chance to join an established family.
Jinn have their own side society.
Use of Jinn in Society
-servants
-labourers(sometimes as animals)
-guards
-caravan guides
-pretty much anything you might ask other people to do for you