From a distance, most of them look so similar to others that you'd need to squint in order to tell them apart. I mostly blame their lack of clear light-dark contrast, and would wish that they were mostly dark with color-coded highlights instead.
Still, even with such a change, the radar symbols look so abstract that, unless you learn about them, you wouldn't even be able to accurately guess what they'd mean from a glance. "Oh? An "X" marks an anti-swarm riot unit you say?" "What does that diamond symbol mean? Oh? An assault unit that wears down base defenses through attrition you say?" "That radar icon that looks like a person is a commander, right? Oh wait, it could also be a Detriment or an Ultimatum you say?"
With this in mind, what if the radar icons were made more clearly-defined, like, say, the various stat boosts that you'd collect in a game of Smash Run from Super Smash Bros 4?
[Spoiler]Here are some examples of how various roles could be made more clear:
- Commander: Flag
- Constructors: Hammer
- Scouts (including Puppy and Owl): Eye
- Most raiders: Boot/foot with speed streaks
- Normal skirmishers: Bow and arrow
- AoE Riots (such as Outlaws, Rippers, Claymores, Venoms, Corsairs, and Scallops): Shotgun spread
- Rapid-fire Riots (such as Reavers, Felons, Archers, Recluses, Maces, Nimbus, and Dante): Front part of a gatling gun barrel
- Assaults (including Sirens and Detriments): Sword
- Precision artillery (such as Slings, Impalers, and Emissaries): Catapult with visible arcing trail
- Saturation artillery (such as Badgers, Firewalkers, Tremors, Merlins, and Shoguns): Hwacha firing off volleys of arrows, or MLRS/Katyusha rocket artillery firing off multiple missiles
- Anti-air: Upwards-pointing dual-barreled anti-aircraft gun
- Suicide unit: Cherry bomb or dynamite stick
- Anti-heavy skirmisher/artillery (such as Phantoms, Racketeers, Lances, and Paladins): Crosshairs
- Heavy gun-equipped siege unit (such as Grizzly, Crab, or Cyclops): A cartoonishly-short and fat cannon with treads/legs
- Transport: Hook and cable
- Drone: Top-down view of a quad-copter
- Drone carrier: Runway
Special cases:
- Scythe/Widow/Ultimatum: Bloody knife
- Iris: Curtain
- Dirtbag: Garbage bag
- Aspis: Shield
- Dominatrix: Heart
- Claymore (alternate symbol): Sea mine
- Djinn: Side-facing portals
- Placeholder: Vortex
- Jugglenaut: Minimalized, miniaturized Jugglenaut with raised leg, as if it's about to stomp on something
- Kodachi: Flame symbol
- Seawolf: Submarine (just as it is now)
- Swift: Boot/foot with speed streaks
- Raptor: Front part of a gatling gun barrel
- Raven: Crosshair
- Phoenix: A series of bombs
- Likho: A mushroom cloud
- Thunderbird: A storm cloud with lightning bolts poking out from underneath
- Gnat: Lightning bolt
- Zeus: Sword with lightning bolt overlay
- Blitz: Boot/foot with lightning bolt overlay
- Venom: Shotgun spread with lightning bolts replacing pellets
- Athena: Hammer overlaying a star
- Dante (alternate symbol): Head with devil horns
- Paladin (alternate symbol): Holy cross
- Detriment (alternate symbol): Skull
- Scorpion: Scorpion
- Scylla: Submarine with missile launching out of back
Finally, here are some ideas for images to apply as overlays for units of different factories:
- Cloakbots: Cape
- Shieldbots: Armored chestplate
- Jumpbots: Jets on the sides
- Amphbots: Air tanks on the sides
- Rovers: Wheels on the bottom
- Tanks: Tank treads on the bottom
- Hovercraft: Hover cushion on the bottom, and air-fans on the sides
- Spiders: Spider head and legs on bottom
- Ships: Sailboat
- Gunships: Helicopter blade on top, and helicopter pontoons on bottom
- Planes: Bird/plane when viewed from below
- Bipedal striders: Person
- Chickens: Zerg-like spike and mandible protrusions