В отсутствие межевого знака вынос границ не начали.

Because в отсутствие is a fixed formal expression meaning in the absence of.

Here отсутствие behaves like a noun after the preposition в, but in this set phrase it is used with the meaning during/because of the absence of something, and the thing that is absent goes in the genitive:

• в отсутствие межевого знака = in the absence of a boundary marker

By contrast, в отсутствии would normally be understood as the prepositional case of the noun отсутствие, used in different structures, and it would not be the normal choice here.

So for this sentence, в отсутствие + genitive is the correct pattern.

Because отсутствие takes the genitive of the thing that is absent.

So:

• отсутствие чего? — межевого знака

That is why both words are in forms that show genitive singular:

• межевого — genitive singular of межевой
• знака — genitive singular of знак

This is very common in Russian with abstract nouns:

• отсутствие документов = absence of documents
• наличие опыта = presence of experience
• нехватка времени = lack of time

Межевой знак is a technical land-surveying term. It means a boundary marker or survey marker that shows where the legal boundary of a plot of land is.

• межевой relates to межа, an old word meaning a boundary line between pieces of land
• знак means marker, sign, or mark

So this is not just any sign. It is a specific marker used in property or cadastral contexts.

You are right: it is a technical expression, not something you should translate word for word.

In surveying and property law, вынос границ means something like:

• staking out the boundaries
• setting out the property lines on the ground
• marking the boundaries according to official documents

Literally, вынос comes from выносить and can suggest taking out, but here it refers to transferring the documented boundary lines into physical reality on the site.

So вынос границ is best understood as a fixed professional phrase.

Because the verbal noun вынос commonly takes its object in the genitive.

So:

• вынос чего? — границ

This is similar to how many Russian verbal nouns work:

• обсуждение проекта = discussion of the project
• проверка документов = checking of documents
• установка оборудования = installation of equipment

Here:

• границ is the genitive plural of граница

So the structure is basically:

• вынос границ = the setting-out of boundaries

Russian often leaves the subject unstated when it is either obvious, unknown, or unimportant.

Here не начали is past tense plural, which suggests an implied they:

• В отсутствие межевого знака вынос границ не начали.
• More explicit: В отсутствие межевого знака они не начали вынос границ.

This kind of plural-without-subject is common in Russian, especially in formal, bureaucratic, or report-like language. It often means something like:

• they did not start
• the workers/officials/company did not start
• it was not started by those responsible

English usually prefers an explicit subject, but Russian often does not need one.

Russian word order is flexible, and this sentence is arranged in a very natural official style.

The sentence starts with the condition/reason:

• В отсутствие межевого знака = in the absence of a boundary marker

Then it names the activity:

• вынос границ

And only after that gives the result:

• не начали

This order helps present the sentence as:

1. under what condition
2. what action is being discussed
3. what happened to that action

A more neutral version with a subject might be:

• Они не начали вынос границ в отсутствие межевого знака.

But the original sounds more formal and report-like.

It can often be understood as either, depending on context.

The verb начать is perfective, so не начали means that the action was not begun.

Depending on the situation, English may translate it as:

• did not start
• have not started
• did not begin
• have not begun

In an official report, it may even imply something like:

• the boundary staking was not initiated

So the Russian form itself tells you the action was not started, but the exact English tense depends on the broader context.

Yes, but the tone and nuance would change a little.

Possible alternatives:

• Без межевого знака вынос границ не начали.
• Из-за отсутствия межевого знака вынос границ не начали.

Differences:

• в отсутствие sounds more formal and bureaucratic, like written documentation
• без is simpler and more everyday
• из-за отсутствия more clearly emphasizes because of the absence

So the original sentence sounds especially appropriate in legal, cadastral, or administrative language.

Normally, no.

This opening phrase is just an adverbial modifier, and Russian does not usually put a comma after such a phrase automatically.

So this is standard:

• В отсутствие межевого знака вынос границ не начали.

A comma would usually appear only if the writer wanted special intonation or separation, but in ordinary formal writing it is not needed here.