>GIS is probably one of the best things to happen to cartography in the last couple hundred years.
GIS is amazing, but the first and second world wars saw a lot of advances in cartography. I'd say #1 advancement goes to the near-perfecting of portable Theodolites. It's a telescope which allows you to look at one point, then look at another, and very accurately understand the angles between them. From that, with a little walking and Pythagoras, you can figure out distances, and thereby create accurate maps with relatively minimal effort and human-error opportunities.
I say "relatively minimal effort" because technique the portable theodolite replaced was sending battalions of civil servants out into the countryside with 50ft long chains and asking them to walk the length, height and breadth of the country.
You still have to send people out into the field. And you had to know what you waned to survey ahead of time. During the war that sometimes meant sending survey teams behind enemy lines. Satellite remote sensing changed all of that.
If you will permit me one cautionary point, given that the deadly Texas flash floods just happened.
The geomorphic reason that there is flat land next to a river is because it is the flood plane. That kind of land looks tempting, but can be deadly. Obviously, GIS analysis could add some kind of distance metric from a river to a usability score, but the analyst needs to know about the problem first.
Just a bit of "ground truthing" from a professional geoscientist.
Everyone that buys a house or land knows these maps and checks them since the last deadly flood happened a few years ago. I cannot believe that the US decided to defund the offices that help to gather these kind of information.
Those flood maps are common across the first world, sometimes called a "flood overlay" and there is usually also a "bushfire overlay" if you live in Australia. They help describe risk, in the insurance sense, and are presumably used for both insurance and risk management.
of course there are flood maps here in the USA. The Federal government does some survey work, but in the US system, it is the county that is responsible for maintaining basic property and land use maps. Every State in the US is composed of county (or parish or some New England thing to be complete). The US Federal government is not defunding "everything". Also note that some parts of the US do not cooperate very much with the Federal government (mostly near Idaho area, others?). Texas regularly discusses becoming their own country, so of course Texas has its own mapping.
Crucially, the thing they was recently de-funded was not mapping but the federal agency that does hydrology. Hydrology being the science of how water flows in the environment around us.
For example, using GIS data combined with meteorological forecasts, a hydrological model may predict water levels of rivers or flood plains. If nobody is around to run the hydrological model on today’s data, you’re not getting your flood warning today.
Any architect and urban planner is aware of the problems with flatlands near river beds. It's the politicians who decide to ignore the science, known since the times of the Romans.
In the US, 3DEP is driving towards high coverage of extremely accurate elevation data, in areas where it has coverage you wouldn't need to use a distance metric really.
Government-subsidized insurance is the opposite of capitalism.
If the market were allowed to operate, no one would be able to afford these houses on the coast. And in many cases that would be a good thing. Instead, the politicians have decided that beachfront property is some kind of fundamental right that we should all collectively pay for.
I think you are sadly correct. Collectivization of beach house insurance, but not health insurance, seems like a rather apt microcosm of contemporary America.
For more advanced terrain analysis, see GRASS GIS (https://grass.osgeo.org/). It’s a but clunky, but accessible from QGIS via a plugin. Whitebox also has some nice terrain analysis tools (https://www.whiteboxgeo.com/).
GIS is truly impressive from a user's perspective: intuitive, powerful, and full possibilities. However, from a sysadmin's point of view, hosting an ArcGIS Enterprise setup - the market leader in this space - can quickly turn into a complex and frustrating experience.
Truth. It’s a pure lock in, so many agencies are committed and sunk so much cost and effort into it that they’re never seriously going to consider any other vendor/solution. The ESRI documentation for any advanced topics falls apart quickly. I’ve spent days with their support liaisons, walking through the steps they have documented and getting different results.
QGIS for ArcMap/ArcGIS
Geoserver for their REST based servers (ArcGIS Enterprise).
GRASS and GDAL do the leg work of much processing found in the spatial toolboxes and such.
However those tools do not have the polish that ESRI kit does, but at leas you’re not paying the licensing!
> However those tools do not have the polish that ESRI kit does, but at leas you’re not paying the licensing!
Arguably they have more polish, but less GUI. The open GIS world is more CLI, database, and library driven, which can be an advantage for many users trying to build high reliability or scaling systems.
The hosted version of, for example, ArcGIS Experience Builder is so buggy and limited that you pretty much have to use the Developer Edition to build anything involving even a mild degree of complexity
I only skimmed it, but I want to point out to the author that in his slope equation, the slope is denoted by m, not x.
But yes, using the Laplacian seems natural as a metric for what he wants to measure. Coming from a physics background though, it felt weird being explained in terms of pixels in a picture what a laplacian is...
Neat. Great to see old-school _actual analysis_, I was worried when I read 'LLM' in the text. Instead, I learned something -- the Laplace operator. The OP's explanation is considerably easier to understand than Wikipedia's :)
GIS is amazing, but the first and second world wars saw a lot of advances in cartography. I'd say #1 advancement goes to the near-perfecting of portable Theodolites. It's a telescope which allows you to look at one point, then look at another, and very accurately understand the angles between them. From that, with a little walking and Pythagoras, you can figure out distances, and thereby create accurate maps with relatively minimal effort and human-error opportunities.
I say "relatively minimal effort" because technique the portable theodolite replaced was sending battalions of civil servants out into the countryside with 50ft long chains and asking them to walk the length, height and breadth of the country.
There's a lot of surveyors marks hammered into things out in the world.
The geomorphic reason that there is flat land next to a river is because it is the flood plane. That kind of land looks tempting, but can be deadly. Obviously, GIS analysis could add some kind of distance metric from a river to a usability score, but the analyst needs to know about the problem first.
Just a bit of "ground truthing" from a professional geoscientist.
Everyone that buys a house or land knows these maps and checks them since the last deadly flood happened a few years ago. I cannot believe that the US decided to defund the offices that help to gather these kind of information.
https://www.fema.gov/flood-maps
For example, using GIS data combined with meteorological forecasts, a hydrological model may predict water levels of rivers or flood plains. If nobody is around to run the hydrological model on today’s data, you’re not getting your flood warning today.
(Sorry for the typo.)
The past 30 years have yielded tons of new hazard maps, but communities refuse to implement them in any meaningful way because of capitalism.
So it really doesnt matter how good our analysis and predictive powers are if the policies are never enforced.
If the market were allowed to operate, no one would be able to afford these houses on the coast. And in many cases that would be a good thing. Instead, the politicians have decided that beachfront property is some kind of fundamental right that we should all collectively pay for.
https://elevation.nationalmap.gov/arcgis/services/3DEPElevat...
Preview in QGIS: https://ibb.co/B5T49YBj
Grade calculations are right in qgis docs and part of their lessons, and are also top Google hits.
https://docs.qgis.org/3.40/en/docs/training_manual/rasters/t...
Even better, you'll learn about DEMs vs topo maps.
However those tools do not have the polish that ESRI kit does, but at leas you’re not paying the licensing!
- former ESRI consultant
Arguably they have more polish, but less GUI. The open GIS world is more CLI, database, and library driven, which can be an advantage for many users trying to build high reliability or scaling systems.
I’ve heard that sentiment before but never understood. Can you elaborate?
But yes, using the Laplacian seems natural as a metric for what he wants to measure. Coming from a physics background though, it felt weird being explained in terms of pixels in a picture what a laplacian is...
https://freegisdata.rtwilson.com/