Hello,
I am new to arduino. I am working on a project to make a smart driving robot. I would like to use geofencing on a small scale (15-20 sqft area) so that my robot will have a reasonable area to navigate. However I am not sure what hardware I would be looking for
is there anything I can use to create geofence on a small scale that my robot can use to locate itself?
In principle any GPS module can be used to determine the robot's position, but the robot must be outdoors with a clear view of the sky.
Unfortunately, GPS positional accuracy is highly variable, and is at best around +/- 2 m, so this approach is very unlikely to work in such a small space.
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We need some more information about your project: What is the accuracy you need? Do you have clear sight to the sky? Can you mark the border with a wire? Can you paint the border?
You can put overhead light over the area, then use a few suitable photo-sensors on top of the robot to detect that light, so if it goes in the dark it takes a few steps back.
Use specific light wavelength or modulate it to avoid interferences.
Any of these are possible
I was thinking of how the roomba comes with little laser flags that you put on doors you dont want it to pass through
This will be an indoor project
Visual markers are fine too.
I was thinking of sensors I could place in four corners of the area/board so that the arduino could effectively “ping” its location and know its position on a x/y plane
And thank you so much for gettin back to me 
i am visualizing items that are effectively beacons that you place in four corners that the arduino can ping off from
It would have been helpful for you to mention in the OP that this is an indoor project. Geofencing is outdoors.
"Indoor localization" is a useful search term, and the process is much more difficult than using GPS outdoors. The best and simplest options are overhead cameras with image processing on a PC, or commercial, broadband beacon positioning networks like Pozyx: https://pozyx.io/
It is easy to say "beacons that the Arduino can ping off from" but very difficult to realize in practice.
Thank you for that, I simply say “beacons” to convey meaning or create an image.
I am new and unfamiliar and I am hoping by painting a picture it will put me in touch with people familiar with what I am trying to accomplish
From that point I will learn more accurate language and technology that is applicable
All search processes start broad when a person is naive (me 
), and narrow as the person becomes more knowledgable as they progress in their search. Basically I dont know what I dont know .
Thank you for indoor-localization, this will help narrow down my search as well as expectations of what is possible, have a great day 
I wanted to let you know your term “indoor localization” has already yielded me more accurate results
Thank you so much
Basically, this is hard. Lots of people would like to be able to do it for warehousing, robotics, undersea navigation etc. etc. etc. Usually, it turns out to be too hard, too expensive or both.
For a small area like yours, where I suspect 100% success isn't crucial, you should be able to make some progress, but it will likely take quite a bit of learning.
I have a different idea that may be more simple
Is there a sensor powerful enough to detect light from ~3 ft away?
I dont believe a phototransistor can do it.
My idea is to run 2 modules instead
1 to detect obstacles and 1 to chase a light source
Photodiodes and phototransistors have unlimited detection range, for a sufficiently powerful light source.
From a point light source, the intensity of the light, and the received signal at the detector, drops off as the square of the distance between them.
If you are thinking of using light sources as beacons, the most challenging problem is to distinguish the beacon from the background illumination. IR or colored LEDs as emitters and appropriate filters on the detector will help.
I was thinking of using a colored LED as I can control that the easiest I believe
My intent is to use object avoidance with laser or sound, and turn my destination into. Light source
In this way i eliminate a coordinate system and instead turn it into a maze more or less
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