Cartography

How far is it?

April 20, 2021 by rjhale

I’ve been working on a cartography project with a little bit of analysis thrown in for good measure. The fun thing is the project forced me down the PyQGIS route. Luckily for you this post won’t cover that. I actually wrote a script and it ran and it did something….it did something wrong but that’s a start.

Anyway – Distance. I had a problem and the problem was “How far are all the canoe launches from the final stop?”. So it’s a networking problem. I don’t care how much time it takes in the canoe – just distance.

I don’t use the network tools often. I’ve done shortest path routing from one location to the other before with mixed results a long time back. I have 9 locations to do. So digging through the tools it appears the Shortest Path Geoprocessing tool will work.

The tool is easy – pick a layer of points. Pick a destination. Pick a network layer which for me is the stream. Running the tool gives you a new layer of data showing the path from your points to the end point. In this case that was 9 lines in one layer for the 9 canoe launches. Each linestring has a cost which is distance. I did a join back to my canoe launch layer and suddenly in a few clicks I have the distance to the end.

From there to a spreadsheet and I have this nifty table showing the mileage from the Lee and Gordon Mill to Camp Jordan The Reeds Bridge Launch to Camp Jordan:

Was all this really worth a blog post? For me yes because I hadn’t done this lately and it was ridiculously easy. Plus this entire exercise has been fueling my PyQGIS itch. As I said earlier I had built some code to do the thing that this did – now I want to do a few things to automate running this on a larger more complicated pile of data. What if I wanted road distance to every fire station from every address? How would I automate that?

…and of course there is pgrouting – Which I’ve been playing with more these days. As I think about it that brings my networking tools to three things: QGIS, Pgrouting, and GRASS.

Anyway – Routing in QGIS is a thing. One more tool in the awesome tool box.

I’m making a Map: Location

December 23, 2020 by rjhale

I should write something. My last few “2020 in Review” posts aren’t working like I’d wish – so I sat down last night to make a map.

A map of what? Good question. I think in my every day attempts of databases and technical wizardry I lose sight of “I actually like maps” and I’m not the best at it. Given my background I should be better. I decided to make a series of maps on “things I like”: Canoeing, Hiking, Bike riding, etc. So my first shot is a canoeing map. A very simple map of something I like to do.

The location is easy – The start of the TN River Gorge. It’s a great 8ish mile paddle. Simple. Quiet.

My first thought was to do what I normally do and just drape things over a aerial photo. I’ve decided to make it a bit more fun and not go that route – This may end up being Black and White. I’m also going to stick to two sizes of paper in this series of maps. Either 8×11 or 11×17.

When you canoe this loop – you start north and head south and loop around an island and then head back north again. The first half is all upstream (heading south) and the last half is all downstream (heading north). Bonus it’s all NW-SE trending so it will need to be rotated.

I start building it in QGIS with some aerial imagery and Hillshades for fun:

If I make a 11×17 layout it looks more like this because I’ve added 120 degrees of rotation:

As I sat here I had a question. I scale it. I generally start to get an idea of “what” I want. I know the extent of the map but can I get the extent back into QGIS so I can start clipping things and not having to include 500 square miles of stuff for a map. I could just set up the boundary back into QGIS as delimited text (make points -> draw polygon). I could just “eye ball it” which is how I do about everything from Jeep repair to Home Repair.

For fun I searched the tool box and….Print Layout Map to Layer

I run that and……I know where my map falls in the main window. So I can buffer it and start clipping data.

Why even post….I had no clue this tool was even here. My next map (another canoeing map) will be a bit larger than 11×17 so I’ll nee to use Atlas to setup 2 to 3 pages. I now have the general extent for 11×17 at X scale, copy and past this boundary a few times, and rotate it to get the general layout locations I will need

Map 1 is well on it’s way to happening. This is a bit therapeutic and that’s something I need at the moment.

QGIS Leader Lines for Labels

May 7, 2019 by rjhale

So way back when…..I was working in a production map shop and I had to make a map of a Nuclear Plant. The fun part being it was all manual. So we would use a lettering machine to place the labels and legend on the enlarged photo. We would manually trace all the features on an overlay.

Flash forward and we’re using ArcINFO and placing annotation and then drawing leader lines pointing to the features on an OrthoPhoto.

Last week and I had the chance to do something I don’t normally get to do: make a cartographic map in QGIS. I needed to make leader/callout lines from the labels back to the polygons. I didn’t want to manually draw in leader lines. Searching led me to two posts:

I ended up running with the kartoza example although both helped me understand how to get this working. So for the not too faint of heart……Here goes. I have some polygons on which I need to “cleanup labels” and leader lines would help in that regard. I could pull the labels away from the very small polygons I have and attach them back with a line.

The key to all of this ais Geometry Generators. The basics are you can use code and expressions in QGIS to draw Geometry. So I’m going to draw leader lines from my label to my polygon with some code (that I copied from Kartoza’s example – Hey to Kartoza). My data is Categorized. So I’m starting off with this:

So I’m going to click on Conservation Easement and add a symbol. The symbol will be a geometry generator. Just as a little background – I’m stacking symbology. So I’m adding another symbol to my yellow symbol by using the plus button on the symbol selector. I’m defining the type as a Geometry Generator and the Geometry Type as a line.

So what happens with the code I so skillfully pasted into the symbol selector?

make_line(
closest_point($geometry,
make_point( “auxiliary_storage_labeling_positionx” , “auxiliary_storage_labeling_positiony” )),
make_point( “auxiliary_storage_labeling_positionx” , “auxiliary_storage_labeling_positiony” )
)

The code says make a line using the closest point on the polygon and anchor it with the location of the label. Now something happens when I use the label toolbar to move my labels away from the polygons:

Now I have leader or callout lines back to my polygon. I’ll need to add a geometry generator to each category to give me lines for every category. The picky side of me is thinking for 100% control I should manually draw them in (but I’m not). If you read Kartoza’s post they have a more elegant final solution to deal with lines running over your labels. Looking at this now I need to move 210 back to the center of it’s polygon since it’s drawing the leader line under the polygon.Overall – Not bad.

Map Competition for Georgia Students

April 20, 2016 by rjhale

…and from Georgia URISA:

Hello Students!

Announcing our

“Online Map Competition”

This map competition it is an opportunity for Georgia University/College students to share their best maps with others who appreciate quality cartography, innovation and finally get recognition for their talents.

This is an online competition. All maps/poster and links need to be submitted by midnight of May 10^thto urisaonlinemapcompetition@gmail.com with a minimum half a page statement that provides context of the submission, i.e. its purpose, how it may be used, how it was created etc…, and a cover page that will include:

Student information, including name, address, phone number, email address.
Degree program (e.g., M.A.), cartography/GIS instructor’s name.
Graduation Date
Institutional affiliation

Maps will be judged based on the following:

Standard Map Elements: Title, legend, scale etc: 15 points
Balance and Layout: Does map appear well-balanced to the eye? Are some areas of the map blank while other areas are crowded: 10 points
Drafting Technical Quality: Technical involvement; difficulties: 20 points
Detail Thoroughness: Is there too little detail? Is there too much detail? Does it extend into every passage? Is it consistent throughout the entire map? Is the detail easy to understand or is it confusing? Does the detail match the legend or the list of symbols? What would be the use of the map? Does the map show the purpose: 15 points
Visual Impact: Does the cartography make the subject interesting or boring? Overall, does the map look good: 20 points
Innovations, new methods which enhance the understanding of the map: 20 points

100 points is a maximum that student can acquire based on above requirements.

First, second and third place will receive a prize. Prizes to be announced soon! The rest of the participants will get recognition in the URISA newsletter and “swag.”

Maps need to be submitted by Midnight of May 10^th to urisaonlinemapcompetition@gmail.com, confirmation email will be an indication of the submission.

QGIS: The Label toolbar

April 4, 2016 by rjhale

You’re sitting in a class…..back up – You’re teaching a class and and someone goes “Hey – there’s this QGIS Label Toolbar. How do it work?”.

I’m probably better at making a map than I believe. I really don’t enjoy it because with every map Green was always a problem. “Can you make this green ‘greener’?”. I would get upset and go “OK” and immediately make it too green. Way back in my career I was working on a Spill Plan Prevention Control and Countermeasures map (I think that’s SPCC). This map was all manual back in the day. We had a plan to make it “digital”. So we scanned a photo (and didn’t georeference it) and started laying out ArcINFO Annotation on it. At some point we scanned another map and had to move everything (not georeferenced) again. Then at some point we decided georeferencing the map was a good idea so I had to move all the annotation. Again. Anytime you say “label this feature” I break out in a sweat to this day.

So I sat this weekend with the whole goal of making the QGIS Label Toolbar Active. The best I could do was this:

I finally “Read the Manual” and found that the label toolbar is Attribute based. So if I add some Attributes to my data layer:

x – decimal number – Length 12 Precision 3
y – decimal number – Length 12 Precision 3
rotation – decimal number – Length 12 Precision 3
visibility – integer – Length 1

…..and then I assign those attributes to the label properties:

…..and then I edit my layer:

I can now move my labeling all over the place to make a better map. I can turn labels off. I can rotate the labels. Of course I’m not even discussing the Rule based labeling and all the joy you can have there.

Anyway – I left a tutorial I need to clean up a bit over HERE that should at least get you started.