ACARA v9 CONTENT DESCRIPTION “create and interpret grid references and maps, and describe positions and movement using coordinates, directions and simple scales”
A grid lets any point be named by two numbers: how far across and how far up. The pair is written in order, across first and up second, so the point three across and two up is (3, 2). The two numbers together pin down exactly one place on the grid, the way a seat is found by row and number. Reading the across value first is the firm rule that stops (3, 2) being confused with (2, 3). Coordinates are the language this whole unit uses, because once a point has an address, it can be plotted, read, and moved with precision.
Plot a coordinate
A coordinate (across, up) names one point on a grid.
Plot the point (3, 2): go right 3, then up 2.
Reading a point's address
Just as a point can be plotted from its coordinates, a plotted point can be read back into coordinates. Count across from zero first, then up, and write the two numbers in that order. A dot two across and three up is (2, 3), never (3, 2), because across always comes first. This reading is the reverse of plotting, and doing both makes the order stick. Being able to move freely between a point on the grid and its coordinate pair is the core skill of grid references, and it is exactly how a map turns a location into something you can write down and share.
Name the point
Read a point's coordinates as across first, then up.
What are the coordinates of the marked point? Read across first, then up.
Directions and turning
Positions also use compass directions: north, south, east and west. On a map, up the page is north, down is south, right is east and left is west. A turn changes the way you face by a known amount: a half turn from north faces you south, a quarter turn right from north faces you east. Combining a starting direction with a turn tells you the new direction without guessing. Directions and turns describe movement and facing, complementing coordinates, which describe exact location, and together they let a position be both named and changed.
Directions and turns
A compass names directions; a turn changes the way you face.
Facing north. After you turn around (180), which way do you face?
Following a path
A route on a grid is a path made of steps along the lines, and its length is the number of unit steps taken. A path from (1, 1) across to (3, 1) and up to (3, 3) is two steps across and two up, four units in all. Following a path segment by segment, and adding the steps, measures how far the route is, not how far apart the ends are. This is how distances along streets or corridors are found on a grid map, and it connects the coordinates of points to the lengths of the journeys between them.
Trace a path
A path along grid lines has a length: the number of unit steps.
Path so far: 2 units. Keep following the route segment by segment.
Naming a movement
A move from one grid point to another has a direction that can be named. Going from (2, 2) to (4, 2), the across value grows while up stays the same, so the move is to the right: east. Going from (3, 1) to (3, 4) keeps across the same and increases up, which is north. Reading a movement as a direction joins coordinates to the compass: the change in the numbers tells you which way you went. This is the skill behind giving directions on a map, where each leg of a journey is a move in a named direction.
Which direction?
A move between grid points has a compass direction.
Moving from (2, 2) to (4, 2), which direction is that?
Maps run on coordinates
Bringing the unit together, a grid map gives every place an exact address as a coordinate pair, and movements between places are described by directions and path lengths. School at (2, 1), park at (4, 3), shop at (1, 4): each is fixed by two numbers, and getting from one to another is a matter of moving so many units in named directions. With points plotted and read, directions and turns understood, paths traced and movements named, a child can both create and interpret a grid map — locating, describing and navigating positions, the practical geometry that maps, games and screens all depend on.
A map by coordinates
Coordinates give every place on a grid map an exact address.
A map can list each place by its grid coordinates. Reveal each one.
Quick self-check
1. The coordinate (3, 2) means...
2. You are facing north and turn all the way around. You now face...
3. A path goes from (1, 1) right to (3, 1), then up to (3, 3). Its length is...
4. Moving from (2, 2) to (4, 2) on a grid is moving...
5. On a grid map, a single coordinate pair like (2, 1) gives a place...