Most people planning a garden are not starting from bare earth. There is already a house, a fence line, a path, a tree that is not going anywhere, and the job is to plan around them. Drawing all of that from memory is slow and it is wrong in ways you will not notice until something does not fit. This lesson is the shortcut: drop an image behind the canvas, tell the editor how big one thing in it really is, and trace. The measurement is the part people skip and it is the part that matters, so we will spend most of the lesson on it. And the thing you measure does not have to be the picture's own edge. It can be anything in the photograph whose real size you know: a fence panel, the long side of your house, or, in the example we are going to use, the dome on the Minnesota State Capitol, which is ninety feet across. There is no special tool for it. Measure across the thing with the dimension tool and type its real size.

Three objectives. First, you will be able to place a reference image on the canvas: a phone photo taken from an upstairs window, a screenshot of an aerial map, a scanned survey drawing, or a sketch on graph paper. Second, you will be able to set the drawing to true scale by measuring something inside that image and telling the editor how long it really is. Third, you will be able to trace the fixed features on top of it, and make the trace exact rather than approximate, using two constraints: a length on an edge and a right angle at a corner. That third one is the new tool in this lesson. The drawing gesture you already know puts the shape roughly where it belongs; the constraints are what make it agree with the tape measure.

This is the sentence to remember from this lesson. A plan that is not at true scale is a sketch, and a sketch will happily tell you that eight tomato plants fit in a bed that holds five. Spacing is the whole reason the editor knows anything useful about planting density, and spacing is measured in real units, so a drawing whose units do not correspond to anything on the ground produces confident, specific, wrong answers. Scaling is one measurement. Find something in the picture whose real length you know, measure across it, and type that length. The picture resizes around what you measured and everything else follows. From then on every number the editor gives you is a number about your actual garden.

Five steps. First, take or find your image. An aerial screenshot from a map service is easiest; a photo from an upstairs window works if the plot is small; a survey drawing is best of all if you have one. Second, place it: the image tool, or the I key, drops it on the canvas behind everything else, centred where you clicked. Third, scale it, and this is the step to slow down on. Take the dimension tool and click across something in the photograph whose real size you know, then type that size. Both clicks land in open photograph, and that is what makes them stick to the picture rather than to the ground. A small blue picture marker beside each end is how you can tell, and like a corner's right-angle mark it shows while you are placing or while the dimension is selected. Anything you have already traced wins the click, so a dimension only attaches to the photo when nothing else could have been meant, and locking the image stops it happening at all. The photo rescales around the middle of what you measured, so the thing you just measured stays put while the frame grows around it. Fourth, trace: back to Region mode, and draw the fixed features on top. Hold Shift as you click and the edge snaps to horizontal or vertical, which is the easiest way to get a straight run straight. Fifth, check. Measure a second thing whose real size you know, and read it, do not type into it. Pick the longest thing you can name for both, because the error in your clicking divides by the span: a fifty-pixel dome is good to a few per cent, a two-hundred-pixel building to about one.

Here is the whole thing on one site. This is an aerial of the Minnesota State Capitol, and the job is a lawn wedge on the mall below the steps. Watch the order. The photo goes down first and lands ten feet wide, which is nothing, because the editor has no idea what it is looking at yet. Then the dome. It is ninety feet across, that is a published number, and two clicks across it and the word ninety turn the picture into a city block at true scale. While you are placing it, each end carries a small blue picture marker saying the measurement is on the photograph rather than on the ground. Then the check, which is the part worth copying: a second dimension along the building itself, which is four hundred and thirty-four feet long by its own figures, reads four hundred and thirty and a half. Nothing was typed into that one. It is a read-out, and it is the only evidence the scale landed. Only then does the tracing start. Down the west walk and along the cross walk with Shift held, so each leg lands on its axis instead of keeping the lean it was clicked with, then close. And then the constraints, which are what make it a plan rather than a sketch. A right angle on the corner, eighty feet on each leg, and the third side reads a hundred and thirteen point one four, which is eighty times root two. That is arithmetic the drawing cannot fake: it comes out only if all three constraints really landed. The picture here carries no markers, because nothing in it is selected. From here it is an ordinary bed, which lesson five fills.

A trace is only ever as good as your clicking, and your clicking is worth about two feet on a satellite photo. That is fine for a hedge and useless for a raised bed you are going to build out of timber. So the editor lets you say what you know instead of clicking it. Two things, and between them they cover most of what a garden is made of. A dimension on an edge: click its two ends, type a length, and the edge becomes that length. A right angle on a corner: click the corner, type ninety, and the corner squares. What makes these constraints rather than measurements is that the geometry moves to satisfy them, and keeps satisfying them. Change one and the others still hold. And here is the part that used to bite: a horizontal or vertical dimension placed on an edge holds the edge on its axis as well as sizing it. Without that, a square corner and two lengths describe a whole family of tilted shapes rather than one shape, and which one you got depended on the order you added them in. It does not any more.

Five steps, and this is the sequence to copy for anything you trace. One: draw it roughly. Click the corners in Region mode, and hold Shift on any edge that is meant to be straight up or straight across, which snaps it to the axis and saves you correcting it later. Two: square the corners you know are square. Dimension tool, choose Angle from the little arrow beside it, click the corner, type ninety. That does not store an angle, it puts the right-angle badge on the corner, which is the same constraint the badge on the canvas toggles. Three: lock the lengths you know. Click both ends of an edge and type its length. Pick Horizontal or Vertical for an edge that runs along an axis, because that kind also holds the edge on the axis. Four: read something back that you did not type. On a right-angled shape the third side is arithmetic, so measure it. Five: if it disagrees, one constraint is missing rather than wrong, and the dimension that is not being met carries a warning triangle telling you which. Add the missing one and the shape settles.

Every edge you have drawn so far has been straight, and most of what is worth tracing is not. Paths curve. Beds curve. The diagonal path that the wedge's third side cuts across curves, and the trace we just made quietly pretended it did not. So here is the rest of the polygon tool. Each side of a shape is a segment, and a segment comes in one of three kinds. A line is what you have been drawing: straight from the last point to the next. An arc bends between those two points along a circle, and the editor works out which circle. A cubic curve bends the way you pull it, and you pull it with the same click that places the point. Nothing forces a shape to pick one kind and stay with it. One bed can be three straight sides and one long sweep, which is what a bed along a curving path actually looks like. The next two slides are the button, the key, and the gesture.

The toggle only exists while you are drawing. Place the first point and it appears beside your last one: two words, Line and Arc, with Line lit. Press A, or click Arc, and the next click adds a curved edge instead of a straight one. That next click is where it gets clever. The arc leaves your last segment travelling in the direction that segment was already travelling, so if you walk up a straight path and then ask for a curve, the curve continues the path. You do not aim it. There is nothing to aim. If there is no straight run to continue, the editor has nothing to work from and falls back to a half circle, which is almost never the curve you wanted. That is what the drag is for. Hold the button down as you place the point, and pull. A handle comes out of the point, the segment becomes a cubic curve, and the direction you pull is the direction the curve arrives. Let go when it sits on the edge you are tracing. Press L, or click Line, to go back to straight sides, and close the shape on your first point.

Three beds, one photograph, one kind of edge each. The photograph is scaled the same way as the last one, from the dome, so these three are at true scale before a single point is placed and the lengths below them are real. The lawn panel on the left is a rectangle on the ground, so it is four clicks in Line mode and nothing else. Straight features do not need anything cleverer, and reaching for a curve here would only make work. The middle bed is the walk corner. Watch the order: up the straight path first, then Arc, then the far end of the curve. Because the arc continues the run it was given, it lands on the paving by itself, and nothing was aimed. That is the whole trick, and it is why the approach matters more than the click that follows it. The bed on the right is that same corner mirrored, and it is the case the arc cannot help with, because the curve is that shape's first edge. There is no previous segment to continue, so the arc falls back to a half circle that misses the path by fifty feet. You can see it appear for a moment, which is worth watching for: it is the editor telling you it had nothing to go on. Then the drag replaces it: hold the button down as the point lands, pull down, and the curve settles onto the paving. Same photograph, same scale, three different edges.

Two minutes of thinking before you trace anything, because the commonest waste of time in this lesson is tracing too much. Ask yourself what on your plot is genuinely fixed. The house is fixed. A boundary fence is fixed. A mature tree is fixed for planning purposes even if you dislike it. A shed might not be; a raised bed certainly is not; a shrub you are considering removing is not. Then ask which fixed things actually cast shade, because those are the ones that will change your planting decisions, and something at ground level like a paved path changes almost nothing about light. And finally ask what you can actually measure, because that is what fixes your scale. If nothing in the image has a length you can be sure of, go and measure something before you start.

Three things. Trace rather than remember: an image behind the canvas costs a couple of minutes and removes an entire category of error from your plan. Scale from something in the picture, not from the picture's own edge, because the size of the frame is the one measurement nobody has and the size of a thing in it is the one everybody does. And constrain what you know, because a trace is worth about two feet and a dimension is worth exactly what you type. You now have a scaled site with its fixed features on it, at lengths you can build from, which is the point at which planning actually begins. The next lesson leaves the drawing tools alone entirely and goes to the plant library, to decide what is going to grow in the ground you have just drawn.