Otdfbt

Tu habites ici depuis un bon moment déjà. J'imagine que toi, tu connais la ville par cœur, à force !

I just picked up this phrase in conversation. Is it close in meaning to "forcément"?

à force

is used in reaction to something said before that the person is doing often or regularly or happened multiple time which would be the cause of something else

It can be translated by "to end up"

- Je vais faire du vélo tout les jour pour aller au travail
- Tu va être musclé à force

- I'm going to cycle to work every day
- You'll end up super muscular

Or it's like making a general statement about a possible future

- C'est la troisième fois que je tombe dans les escaliers
- Tu vas te casser une jambe à force

- That's the third time I fall in the stairs
- That's how you'll break your leg

Can also be used ironically

- Papa, tu peux me filer 10 euro pour mon déjeuner
- Tu va me ruiner à force

- Dad, can you give me 10 euro for my lunch
- You'll ruin me

I wouldn't say that it is close in meaning to "forcément" (which is a bit like "of course") even if it has the same origin (force = strength). This comes from "à force de", used as a preposition but, in this case, there is an "ellipse". So the original sentence should be something like, e.g.

J'imagine que tu connais bien la ville à force de la parcourir à pied tous les jours.

That being said, "à force de" means "by doing a lot of", "by making a lot of effort for". In your sentence, this would mean that the person has spent a long time in the city or something like that (because of the "ellipse", it is not possible to know exactly what is meant without a bit of context). For instance, it could also be "à force de lire tous les guides touristiques que tu trouves".

La locution adverbiale à force est synonyme de à la longue (TLFi) ou par des efforts répétés (Larousse en ligne). Ac.9 indique vieilli pour au moins le sens extrêmement.

De plus, en menaçant toujours sans frapper jamais, à force, on aura
fait le jeu de l'Allemagne. (Jaurès, au TLFi)

I would say it is a popular expression, to emphasize repeated or long-term duration events.

"À force de faire ça, tu vas ... " -> "Doing that again and again, you will ... "

In your example :
"Tu connais la ville par cœur, à force." -> implicitely means "You know the town by heart, ... living here for such a long time" , but it could also mean "You know the town by heart ... visiting it again and again", etc. depending on the context.

Actually, it is a quite ambiguous expression, so don't worry if it is confusing, as it can be for french people as well, but we are so used to it that we don't even ask ourselves questions about it. :-)

Ça vient du sens .3 de à force de

En refaisant, en faisant beaucoup

Ici, le [de + infinitif] est sous-entendu. C'était probablement évoqué plus tôt dans la conversation (à force de travailler ici, à force de la visiter, ...) mais on peut souvent le déduire du contexte.

Autre exemple. Ces deux phrases ont grosso modo le même sens :

À force de l'écouter tous les jours, je connais les paroles par cœur.

Je l'écoute tous les jours, je connais les paroles par cœur, à force.

No, it's not close to "forcément"; "à force" is an elliptic phrase which is more often, if not to say more properly, formulated as "à force de X"; this is rendered in English by "by dint of X".

A preferable phrase would be specific ;

• à force de trainer dans les rues


• à force d'en sillonner les rues


• à force d'y travailler avec ton taxi
  
  …

The elliptic form can be used when the omitted part has just been discussed or mentioned;

• Ils vous changent de quartier régulièrement alors, tu ne distribues jamais le courrier trop longtemps dans le même quartier ; tu dois connaitre la ville par cœur, à force. (à force de faire de nouveaux quartiers.)

If we were to say "J'imagine que toi, tu connais la ville par cœur, forcément !", what would be meant is that one of the reasons for knowing well the streets (X), a reason the interlocutors are clearly aware of in the given context but that they haven't necessarily stated in the conversation, makes inescapable a thorough knowledge of the city.

"Forcément" means "necessarily", "inevitably".