Depending on the type of map you are referring to, the solid black line could indicate a national boundary. If it is a map of states, it could be a state boundary.
For many maps, major cities (e.g. population over 1,500,001) use a large solid black circle as the symbol. Cities with populations 1,000,001 to 1,500,000 and cities up to 1,000,000 each use a smaller solid black circle. State capital often uses a solid black star symbol on a map.
The Key, or Legend, or a map gives a list of the symbols used on the map and what they represent. There is a fairly standard set of symbols used for different types of map so that anyone looking at the map can understand what it is being shown. For example, on a weather map a cold front is shown as a black line with semi-circular bumps (in blue if coloured), a warm front is shown as a black line with triangles (in red if coloured) and an occluded front is shown as a black line with alternate semi-circular bumps and triangles.
Is it X? Brought to you by xrehabv4
A contact line on a geologic map is noted by a solid or dotted horizontal line with breaks sectioned off by a small vertical line below it. A fault line is noted as a horizontal dotted line with wide dashes.
The equator is located at 0 degrees latitude on a map grid, dividing the Earth into the Northern and Southern Hemispheres.
Depending on the type of map you are referring to, the solid black line could indicate a national boundary. If it is a map of states, it could be a state boundary.
boarders
A national boundry is a thick black line
The national boundaries
It is common for a map "key" or legend to gauge the size of cities on a map. For example, a city with a population of over 200,000 may be marked by a black dot surrounded by a black bordered circle line. White is the shade between the black dot and the black line of the circle.
Contour lines on a map are typically brown or black in color. They indicate elevation changes on the map.
For many maps, major cities (e.g. population over 1,500,001) use a large solid black circle as the symbol. Cities with populations 1,000,001 to 1,500,000 and cities up to 1,000,000 each use a smaller solid black circle. State capital often uses a solid black star symbol on a map.
The Key, or Legend, or a map gives a list of the symbols used on the map and what they represent. There is a fairly standard set of symbols used for different types of map so that anyone looking at the map can understand what it is being shown. For example, on a weather map a cold front is shown as a black line with semi-circular bumps (in blue if coloured), a warm front is shown as a black line with triangles (in red if coloured) and an occluded front is shown as a black line with alternate semi-circular bumps and triangles.
Is it X? Brought to you by xrehabv4
A contact line on a geologic map is noted by a solid or dotted horizontal line with breaks sectioned off by a small vertical line below it. A fault line is noted as a horizontal dotted line with wide dashes.
The "X" on a Delta seat map typically signifies a seat that is unavailable or occupied.
The equator is located at 0 degrees latitude on a map grid, dividing the Earth into the Northern and Southern Hemispheres.