With the Raspbian Buster image downloaded and your SD card inserted into your Mac, it's time to flash the disk image.
Open Disk Utility and find your SD card
To open Disk Utility, in Finder navigate to Applications > Utilities > Disk Utility. If you're SD card is inserted correctly, it should appear on the left hand side of the application.
Format the SD card
Click on the name of the SD card in the left column of Disk Utility.
Click the "Erase" button.
Choose a name for the card (any name will do as long as you can remember it), then choose MS-DOS (FAT) for the format.
Click Erase to complete the process.
Determine the mount point
df command (in Terminal) we're going to determine the mount point.
In the output, under the Mounted on column look for the name of your SD card. I named my BUSTER so I'm looking for /Volumes/BUSTER.
Then take note of the filesystem name in the first column. Mine is /dev/disk2s1. This is actually the partition name, but what we're really concerned with is the device name which is disk2. Copy this device name.
Unmount the volume
For this step you can use either Disk Utility or Finder. In either case look in the left column for the name of your SD card, and click the eject symbol.
Locate the Raspbian Buster disk image
By default, your disk image should be in your Downloads folder. We're going to use Terminal to find the disk image, unzip, and get the name of the img.
ls -lha | grep -i buster
You should see output like this:
[Downloads]$ ls -lha | grep -i buster
-rw-r--r--@ 1 tyler staff 346M Nov 8 14:51 2019-06-22-raspbian-buster-lite.zip
This will create a new file called 2019-06-22-raspbian-buster-lite.img.
Flash the disk image
Still in Terminal, type:
sudo dd bs=1m if=DISK_IMAGE_NAME of=DEVICE_NAME
Make sure to replace the values for DISK_IMAGE_NAME and DEVICE_NAME. Mine looks like this:
sudo dd bs=1m if=2019-06-22-raspbian-buster-lite.img of=/dev/rdisk2
Enter your password, and wait. After the process completes, you're done!
Note: You may have noticed that we're using rdisk2 instead of disk2. You can actually use either, but rdisk2 is significantly faster.