[Qgis-user] How to create a QGIS grid but not the usual way

[Thayer Young]

 Hi John,
You may want to start by using the QuickMapServices plugin to add a basemap like OpenStreetMap. I suggest OSM because it tends to have administrative boundaries like counties. To make sure that everything is lining up correctly.
Then with your extent polygon:You can turn snapping on so that the measure tool snaps to the corners of your extent polygon.  View: Toolbars: Snapping Toolbar  <-- make sure that this is checked.Then click on the "Enable Snapping" icon, which looks like a red horseshoe magnet with white tips (you can also just press the S key).Then, click on your Extent layer to make it the active layer in the layer panel. Then set the other icons to the right of Enable Snapping as follows: "Active Layer", "Vertex", "6", "px"  
You should then see that your cursor for the measure tool changes to a magenta square when you hover over the corners (the vertices) of your extent polygon.
You may need to reproject or define your projection:It sounds like you probably have an extent that is in state plane, QGIS often has problems recognizing state plane projections. You can try to export your extent to a projection that QGIS understands, for example NAD83 UTM zone 17N or 18N depending on where your county is in North Carolina. Otherwise try the set projection tool.
Right click on the extent layer, left click Export then left click Save Features As. In the dialog you can set the projection.  
-Thayer

Date: Sat, 15 May 2021 12:05:53 +0000 (UTC)
From: John Antkowiak <john_antkowiak at yahoo.com>
To: "qgis-user at lists.osgeo.org" <qgis-user at lists.osgeo.org>
Subject: [Qgis-user] How to create a QGIS grid but not the usual way
Message-ID: <1021879306.860570.1621080353872 at mail.yahoo.com>
Content-Type: text/plain; charset="utf-8"

Hi. I'm new to QGIS. I've been up all night reviewing the Training Manual and watching tutorial videos looking for someone to address my situation. I'm overtired and I'm sure I'm missing something obvious.
I'm trying to create a large-format paper wall map to show all the roads in my county, and I have to create an atlas to do it.
For sake of this question, let's assume the county is approximately 19 miles east-west and approximately 28 miles north-south. The key word here is approximately - and I suspect this task requires precision that I don't know how to find.?
All the lessons for creating grids from which the atlas will be generated instruct me to do it the same way: specify the desired horizontal and vertical intervals. That's not what I want.
What I want is to divide the extent by three, whatever interval that happens to be. And I can't figure out precisely the total dimension, in miles, of the map extent. In case this is relevant: the data layers are projected in?NAD83 / North Carolina (ftUS) but the QGIS GUI at the bottom right says "Unknown CRS."?
I created a layer for this exercise - don't ask me to explain how I did it - whose only feature is a rectangle covering the area to be divided. This layer I call "Extent."
I try to use the Measure tool to get the exact east-west distance of the polygon. BUT. I have to manually select the start and end points, and I have no confidence that the points I'm selecting precisely match the limits of the polygon because when I measure the north and south horizontal lines, I get two different values. It's a rectangle. The values ought to be the same.
Am I going bout this all wrong? How do I create this 3 x 3 grid?
Thanks -?
John A.
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