That area identified as Downtown on the map provided is actually the Downtown
Neighborhood (an area of mostly historic residences, some dating to the 1880s), which is distinct from the downtown area of Albuquerque. It's also known as the Fourth Ward Historic District. Fourth Ward sounds like the name of an area in a hospital or an insane asylum, so I think that's why the name was officially changed to Downtown Neighborhood.
Downtown Albuquerque is located west of the BNSF railroad tracks, east of 6th Street, north of Coal Avenue and south of Marble Avenue. Those are the generally accepted and easily identifiable boundaries of the majority of Downtown Albuquerque. You of course have adjacent areas that are sometimes referred to as downtown and which many do consider downtown such as the area east of the BNSF tracks and west of Broadway, and the area around 8th Street and Silver Avenue. Then you have the area known as EDo (East Downtown) which runs east of Broadway to I-25 along Central Avenue.
A quick way to find the heart of Albuquerque is to find the place where the city's four quadrants meet and that is at the BNSF railroad tracks and Central Avenue. This is the area where a new town site was laid out in the 1880s when the Santa Fe railroad first laid its tracks through the Rio Grande Valley. This new town was separate from the original settlement known as Albuquerque, but still carried the name. It was referred to as New Albuquerque or New Town for a while and eventually overtook the old town in prominence and thus generally came to be known simply as Albuquerque. The old settlement, which dates to 1706, came to be known only as Old Town. Today Old Town is merely an area of the City of Albuquerque (it was annexed in 1949) and that new town created in the 1880s is now known as Downtown Albuquerque.
The city's old ward system was the precursor to the quadrants used today. The 1st Ward was the area of the city northeast of Central Avenue and the railroad tracks, the 2nd Ward the area to southeast, the 3rd Ward the area to the southwest and the 4th Ward the area to the northwest (hence the name 4th Ward Historic District).
All addresses in the city will have the quadrant initials included (NE, SE, NW, SW). So an address of say 5301 Central Avenue NE means that it is 53 blocks east of the railroad tracks and on the north side of Central Avenue, since it is the north-south dividing line.
Here is a satellite map on Google centered on the point where the quadrants meet:
https://maps.google.com/maps?q=Downt...ew+Mexico&z=15
And here it is zoomed in a bit to show more clearly where the downtown area is:
https://maps.google.com/maps?q=Downt...ew+Mexico&z=16
It's somewhat centered on Civic Plaza, which is where City Hall is located. But the actual center or heart of Downtown is usually considered to be at 4th St. and Central Ave. This is the only place in the country where Route 66 intersected itself. The way that happened is that the original alignment of Route 66 had it going north-south through Albuquerque along 4th Street. It was changed in 1937 to an east-west route along Central Avenue.
Here is a map showing both of the alignments through town (Route 66 in red where it doesn't follow modern-day I-40 or other highways still in use):
https://www.google.com/search?q=rout...ml%3B450%3B294