That is the correct first-order least-squares fit. But I think in your plot the '.' marker on the far left side is coincident with the y axis. The result is it looks like the fit is off. Try using 'o' markers instead, as shown below.
Also, as a general practice to help with debugging these kinds of things, I recommend trying not to change variable names unless there's a really compelling reason to do so. Setting x=lon and y=lat just adds confusion. It's particularly confusing in this case because the syntax plot(f,y,x) plots y on the x axis and x on the y axis, but automatically labels the x data as y, and labels the y data as x. I recommend this rewrite:
lat = [30.4056270000000;30.3991500000000;30.4000740000000;30.4046990000000;30.4102510000000;30.4093280000000;30.3889660000000;30.3982300000000;30.4074760000000;30.4195050000000;30.4139500000000;30.4120980000000;30.4083980000000;30.3936010000000;30.3926810000000];
lon = [40.7602680000000;40.7609660000000;40.7616710000000;40.7623780000000;40.7623830000000;40.7602710000000;40.7644750000000;40.7574480000000;40.7616770000000;40.7609820000000;40.7637930000000;40.7651980000000;40.7637880000000;40.7595540000000;40.7560360000000];
f=fit(lat,lon,'poly1')
plot(f,lat,lon,'o')
xlabel latitude
ylabel longitude
Or, if you want to keep longitudes on the x axis, as is common, this:
lat = [30.4056270000000;30.3991500000000;30.4000740000000;30.4046990000000;30.4102510000000;30.4093280000000;30.3889660000000;30.3982300000000;30.4074760000000;30.4195050000000;30.4139500000000;30.4120980000000;30.4083980000000;30.3936010000000;30.3926810000000];
lon = [40.7602680000000;40.7609660000000;40.7616710000000;40.7623780000000;40.7623830000000;40.7602710000000;40.7644750000000;40.7574480000000;40.7616770000000;40.7609820000000;40.7637930000000;40.7651980000000;40.7637880000000;40.7595540000000;40.7560360000000];
f=fit(lon,lat,'poly1')
plot(f,lon,lat,'o')
xlabel longitude
ylabel latitude
