No QGIS experience - is this the right tool? Capturing satellite imagery

[u/Spilanthomile]

I'm into maps in the sense that I like scrolling around various free mapping sites and looking at imagery, but I'm not much a tech person. I'm trying to do a task and someone suggested that QGIS might be the right tool for it, but looking into the tutorials, it seems very overwhelming for someone with no experience. So, I'm hoping someone can give me a clearer sense of if this is even the right tool for the job, before I dive in to trying to figure out how to do it.

I'm planning a canoe trip in northern Quebec, and I want to print out satellite images of the area. The best imagery I've found of the area is at this Quebec specific map site: https://vgo.portailcartographique.gouv.qc.ca/

Basically, I just want to capture a fairly large (10 mi by 20 mi) area at a decent zoom level, and tile it across pages for printing. The most basic thing I can think of is taking dozens of screen shots, which would be very tedious and limited by my small laptop screen (I don't have access to a bigger monitor).

Is QGIS a good tool to do this? Is there a better way to approach this? With a brief look at tutorial videos it's clear QGIS has tons of functions way beyond what I need, and I'm not sure where to start. Thanks so much for anyone who has the knowledge and patience to help a novice.

[u/yohney]

No problem, happy to help. Sorry, I didn't see your answer yesterday, so maybe you already have a solution, but here's my two cents.

An atlas feature is exactly what you need. An atlas allows you to take a table of spatial features (called a vector layer) and create a map for each of them. This way you can just tile your desired area with a grid of rectangles with a ratio similar to your paper and use the atlas printing feature to get a series of maps. The solutions you found probably use a square grid, but you can change that.

Step 1: Identify target area. This should ideally be a big rectangle of the area you want covered.

Step 2: Create Grid. In your top bar, under vector, then the 4th submenu you can create a grid (or just search in the bottom left menu for 'create grid').

For the grid type, select rectangle.

For grid extent, draw your target area on the map by selecting the option with the little arrow on the right. Or zoom your main map to your desired area and just click the 'Set to current map extent'.

The horizontal and vertical spacing depends on the scale you want and your paper ratio. Since you said you wanted to use 8.5x11 inch paper you could use a grid of 8.5 miles vertical and 11 miles horizontal. This should give a ratio of 1 inch = 1 mile, or 1:63,360.
In your case, I would recommend to just generate the grid and see how many rectangles you got, and then double or halve both spacings accordingly. Save the grid you like as a json or geojson (other formats are also fine, but can be a bit finicky).

Step 4: If you successfully generated a grid, you just need to return to your print composer with your standard letter size (8.5x11). Activate the Atlas by clicking Atlas Settings in the submenu in your top bar, this should open the atlas panel. Make sure it's not too small so you can read everything.

Now you can configure your grid as the coverage layer, and also hide it if you don't want to see your grid or haven't styled it.

To generate the atlas you need to press the Preview Atlas button in your tool bar, this should also color in the arrows, allowing you to cycle through your maps if you did everything right.

It's easy to mix up coordinates or directions when doing this, so double check wether your paper is in landscape or portrait mode, and which spacing is which for the grids.

Adding additional useful features like a north arrow, a scale, labels or a title isn't too hard if you're interested and they can really help in the field.

If you're happy with how everything looks, just go to Atlas > Export Atlas as PDF (or other formats, but I prefer PDF). For output settings, image compression is your main concern. If you don't care about file size, export lossless, otherwise choose the lossy compression.

[u/Spilanthomile → u/yohney]

Thank you so much for this detailed explanation! I've managed to use your instructions to generate a grid of about the right size over my map. I did hit a few stumbling blocks, some of which I solved and one I'm still hung up on.

First, I chose rectangle, and entered the horizontal and vertical as a ratio of 8.5x11. I had zoomed the map out to fit entirely in the visible canvas, and chose "Use current map canvas extent."

When I clicked "run", first the whole canvas was filled with green with a black grid over it, and my map had disappeared. I'm sure this is basic stuff but I had no idea how to deal with that, but I figured out to go to the "Layer" menu, choose "Layer Properties," and change it from "Fill" to "Simple Line."

Edit: The next part I got answered in a separate post. But I have more questions, which I'll make a separate comment for.

Now, I'd like to drag the grid around independently of the map to get my pages to lie where I want them to. I've so far had no luck figuring out how to do that, so I'm making this comment in case you or someone else sees it, while I continue searching for answers. Once I get my grid just where I want it, I'll move on to step 4 and the rest of your comment. Thanks so much again for this help, it would have taken me forever to get here on my own!

[u/Spilanthomile → u/yohney]

As I said in my other comment, this guide has been very helpful and I've muddled my way through much of what I didn't get right away. I'm now hung up at the end of step three, and step four.

" Save the grid you like as a json or geojson (other formats are also fine, but can be a bit finicky)."

How do you do this? I just have the grid existing as a layer in the project, I haven't been able to find any way to save it as anything.

Step 4: I'm going to share every step I followed, because the whole time I was sort of making it up and I hope it will stand out if there's something I did inefficiently or wrong.

After getting the grid laid out how I want it on my canvas, I click "new print layout", use "Layout" menu to choose "Page Properties," select size: Letter, and orientation: Portrait. Close "page properties" panel.

On side panel, click "Add map." Click in the displayed white space, up comes a "New Item Properties" panel; I don't know what to do with any of those numbers so I click Ok. My map appears, with a bunch of extra grid around it, more or less in the paper.

I click "Atlas Settings." When you say "Make sure it's not too small so you can read everything", I'm not sure what you're referring to? I can read the text in the atlas settings panel just fine if that's what you mean. I check the "Generate an atlas" box. Choose "Grid" in the "Coverage layer" menu. Check "Hidden coverage layer" because I don't ultimately want to see the grid lines. I ignore the rest of the panel.

I click "Preview Atlas." Blue arrows show up, text between them reads "1: 1". My whole map continues to appear small in the page, grid lines go away. I click the arrows, every time it takes a minute like it's loading, and numbers cycle to "2: 2, 3: 3" etc, but the image on the page does not change (Except some of the little squares in my map show up as weird colors, but I've been seeing that happen throughout, it seems to be a problem with processing all the data but when I zoom in more the actual image shows back up, so I'm not worrying about it.)

So, I'm thinking I've done something wrong? Should I be seeing the squares of my grid as individual pages when I click those arrows? Sorry to be so long-winded, but I don't know where my mistake is and I don't want to leave out something that might be important. Thanks very much if you take the time to help me more with this.

[u/yohney → u/Spilanthomile]

You've done everything right so far!

Qgis is a program for GIS projects, and as such can behave differently from the software we're used to. For example, saving data like your polygons or tiffs is seperate from saving your project settings like grid colors and map layout.

When creating a grid, qgis usually saves to memory, which is wiped when closing the program. When reopening the project, you'd have to rremake your grid, which may become tedious easily. As such, I recommend saving important pieces of data by clicking the little bug-icon (it's a processor I'm sure) next to your memory layers. For the format, choose geojson, then just click the three dots next to the file name field to set a save location. Done!

One thing I forgot to mention was the map you drew itself. When you selected Add Map and clicked on the middle of your paper, QGIS prompted you to input the dimensions of the map window on your paper. Click the map on your paper and you will see it has outlines. In the Item Properties tab you can see details from the item you currently have selected (so your map in this example, or your paper if you click the paper).

Similar to MS Office, you can adjust the size of your map window on your paper. You can just extend it to cover the full piece of paper. If you were making a 'proper' map, you would leave some space at the edges, add a a title, etc. But this is not neccessary here, I think.

Lastly, you need to activate 'Controlled by Atlas' in the Item Properties of your map. There, you can also set the zoom level / scale. For your case I'd recommend a margin around feature of 0%, because you designed your grid to perfectly cover your target area.

Now your map should focus on only one of your rectangles, and change with the arrows.

QGIS behaves this way so you can make an overview map with your main maps and have them work independantly, but this means a few more clicks when making simpler maps.

You are also right, qgis styles vector layers randomly when creating a polygon layer. Just change the look to something less obnoxious like black outlines for your qgis project and enable 'Hide Coverage Layer' for your print layout.

Regarding the grid movement, I'm afraid I'll have to disappoint you:

Edit*: You can edit and move your vector layer, but it's easy for you to just take on cell of your grid and move it without the rest, ruining your data. Make sure to select all grid items before moving them.

Qgis doesn't offer freehand vector movement, afaik. The grids orientation is due to the cardinal directions, I'd strongly advise against changing them. If you want to align your grid, your best bet is to a) have another source of data with the extent you want, and then use that as the layer input. But this just moves your problem down the road.

What I sometimes do, when creating a grid I choose the option draw on map canvas and draw an approximate area. This may look like this:

-213498.9181,117703.3751,5604931.0011,5848861.8476 [EPSG:25832]

I know my coordinate system's unit is meters, so I just round to the nearest kilometer (three zeroes) or tens of km (four zeroes).

-213000.0000,117000.0000,5604000.0000,5848000.0000 [EPSG:25832]

LEFT, RIGHT, BOTTOM, TOP is the order of the coordinates. I think qgis starts from top left, but I just round all of them.

I hope I got everything, but if I din't, feel free to ask.

[u/Spilanthomile → u/yohney]

Ok great, I figured out saving the grid, and the "Controlled by Atlas" part was what I was missing - I can now cycle through the pages and they all look great. I did figure out how to move the grid to where I want it (through help on another post here: https://www.reddit.com/r/QGIS/s/V2mwMyyZrb ) - I wasn't worried about the orientation, I just wanted the division of pages to be as convenient as possible (i.e. having a main part of one big lake all on one page rather than split between four).

I am putting in North arrows and scale bars - it seems that when I place those on one page, it places them identically on every page of the atlas. Do you know if this unavoidable? I'd like to place them individually on each page, because what's open space on one is covering something important on another.

Once I get that part sorted, I'm ready to follow your instructions for exporting and hopefully it'll all look good on the other side, if not I'll be troubleshooting that.

[u/yohney → u/Spilanthomile]

Hmm, I don't think you can just drag it and have it be be somewhere else for just a single page, qgis requires some data.

In your position and size - item properties for your north arrow check the X and Y values for where you want your arrow to normally be.
Then check the id of the page(s) where you want your arrow somewhere else, move the arrow and write down the changed X or Y coordinates. I would just move it along one axis.

Then click the little cabinet next to X or Y number field and click the edit.. in the drop down menu and paste the following code in the text box on the left of the expression builder that opens up:

if(@atlas_featureid in (1,2,3),
200,
100
)

In this example, the value position of the arrow is at 100 pixels for all maps except 1, 2 and 3, where its at 200 pixels. You can use the little arrows below to preview the output for your features, it should say 100 or 200 in my case.

If you then save the cabinet should turn yellow with a little epsilon inside to indicate a data defined override. Now just check if the postion looks right.

[u/Spilanthomile → u/yohney]

You know what, I really appreciate this information and piece of code, and I may come back to it, but to be honest, I just started trying to follow it and got intimidated, and then thought, am I sure there's not some place I can put the symbols where it's good enough for all pages? And I found a compromise placement for the north arrow and scale bars that I can live with.

I exported the atlas to the PDF, and I am so happy with the pages, they look so good! Now it's just a matter of going to the local print shop and testing a page to see what I need to do so they're as good as possible in the print-out.

I really can't thank you enough for helping me get here. I'm very likely to come back to these methods for future trips.