Visibility

Visibility is the maximum number of squares away from the player that an orb can be while still being shown on the screen. In the Java RuneScape client and the emulator, visibility is 15 squares. That is, if you are at position (x, y), then the visible orbs are precisely those with coordinates (x', y') where x' is between x - 15 and x + 15, and y' is between y - 15 and y + 15, inclusive. Some of the specific implications of visibility are: On the NXT client, visibility is 31 squares, so this is one advantage of the NXT client over the Java client.
 * On the mind altar, the leftmost spawn is at x-coordinate -16 and the rightmost spawn is at x-coordinate 15. This spans a length of 32 squares, while from any position your visibility only spans a length of 31 squares. This means that there is no possible position on the mind altar from which you can see all possible spawns. Thus, no matter where you are, there is always a chance that an orb will spawn and you have no idea where it is until you move elsewhere.
 * The same issue is true of the earth altar, where now the vertical direction also poses this issue, instead of just the horizontal direction, as the y-coordinates of spawn locations on the earth altar range from -16 to 14.
 * On the water altar, when playing green, there is a starting spawn location at x-coordinate 16 which is not visible from the usual center south or north positions. Also, on both colors, there are 8 far south spawns are not visible from center north.
 * On the body altar, when two players play north/south, the spawn at (-16, 5) is invisible to both of them.

Maximizing visibility
The following are the places to stand in order to maximize visibility on each altar:
 * Air altar: This altar has no visibility problems.
 * Mind altar: (-1, -2). From this location, exactly 10 spawn locations are invisible, all on the east side, between (15, -9) and (15, 1).
 * Water altar: Any of (0, -2), (1, -2), (2, -2), (2, -1), and (2, 0).
 * Earth altar: (-1, -2). From this location, exactly 15 spawn locations are invisible; 12 on the east side and 3 on the north side.
 * Fire altar: This altar has no visibility problems.
 * Body altar: Anywhere with x-coordinate between -5 and -1.

General tips
When soloing, when you want to survey the altar to find where all 3 spawns are, run around the altar in a full circle. All spawn locations will be visible to you at least once while you are doing this.

When duoing, always make sure that every spawn location is visible to at least one of you. In particular, avoid having both players be on the same side of the altar, either vertically or horizontally.